Evidence Library
Peer-Reviewed Open-Access Research on Botulinum Toxin Safety and Systemic Effects
Tox Safety's Library
Use the search bar at the top of the page to find specific topics or studies.
This evidence library organizes peer-reviewed studies, clinical case reports, and mechanistic research related to botulinum toxin. It includes evidence on systemic effects, neurological findings, diffusion, structural changes, and reported adverse outcomes.
The goal of this library is to provide a centralized, structured reference point for exploring the scientific literature. Readers are encouraged to review original sources and interpret findings within the context of study design, dosage, and clinical application.
Please note: we only provide open-access research for download.
Featured Evidence
Selected studies with strong clinical and mechanistic relevance
Adverse Events
2025
Cross-Sectional Survey Study
Findings From the Great British and Northern Ireland Botulinum Toxin Survey: Treatment Outcomes, Patient Experience, and Regulations From a Cross-Sectional Survey
A national cross-sectional survey of 919 individuals receiving cosmetic botulinum toxin injections, identifying both acute and long-term complications, gaps in informed consent, and significant variability in practitioner qualifications, highlighting real-world safety concerns and underreporting of adverse events.
Adverse Events
2024
Case Series
Iatrogenic botulism after botulinum toxin type A: Five cases
Case series of five patients who developed systemic botulism symptoms including ptosis, dysphagia, respiratory difficulty, and generalized muscle weakness following botulinum toxin injections for cosmetic, hyperhidrosis, and obesity indications, with several cases requiring antitoxin and demonstrating dose-related severity.
Mechanism / Clinical Overview
2023
Clinical Reference / Review
Botulism Antitoxin
Comprehensive clinical overview of botulinum toxin describing its mechanism of action, pharmacology, clinical uses, and potential adverse effects. Botulinum toxin inhibits acetylcholine release at the neuromuscular junction, leading to localized paralysis, but may also produce systemic effects through diffusion or unintended spread. Reported adverse effects include dysphagia, generalized weakness, respiratory compromise, and autonomic symptoms, particularly at higher doses or in susceptible individuals.
Mechanism
2018
Review (preclinical + clinical evidence)
Direct Central Nervous System Effects of Botulinum Neurotoxin
Review of experimental and clinical evidence demonstrating that botulinum neurotoxin type A undergoes retrograde axonal transport into the central nervous system, with subsequent transsynaptic spread and measurable functional effects beyond the peripheral injection site, challenging the assumption that its action is purely local.
Adverse Effects
2018
Review (perspective/narrative review)
Mandibular Bone Loss: A Hidden Side Effect of Botulinum Toxin Type A Injection in Masticatory Muscles
Reviews evidence suggesting that botulinum toxin injections in masticatory muscles may lead to mandibular bone loss through muscle atrophy and reduced mechanical loading, with supporting findings from animal models and limited human imaging studies.
Mechanism
2016
Animal Study
Interneuronal Transfer of Botulinum Neurotoxin A After Peripheral Injection
Experimental study demonstrating that botulinum neurotoxin type A can undergo interneuronal transfer following peripheral injection, moving from primary motor neurons to connected neurons within the central nervous system. The study confirmed cleaved SNAP-25 in second-order neurons, providing direct evidence of transsynaptic spread and functional toxin activity beyond the initial injection site.
Clinical
2010
Case Series + Review
Systemic Weakness After Therapeutic Injections of Botulinum Toxin A: A Case Series and Review of the Literature
Case series and literature review describing systemic effects of botulinum toxin type A characterized by generalized muscle weakness distant from injection sites. The paper presents three patients who developed widespread weakness, dysphagia, gait instability, and functional decline following therapeutic injections, despite prior tolerance of similar doses. Electrophysiological findings confirmed denervation in non-injected muscles, supporting systemic spread. The review suggests that total dose and injection frequency may contribute to risk, with repeated high-dose injections increasing the likelihood of systemic toxicity.
Adverse Events
2025
Observational Study
Analysis of Clinical Challenges and Prognostic Risk Factors for 195 Cases of Iatrogenic Botulism
Analysis of 195 cases of iatrogenic botulism identifying common early neurological symptoms, including blurred vision, ptosis, fatigue, and dysarthria, along with complications such as aspiration pneumonia, highlighting real-world risks associated with botulinum toxin exposure.
Adverse Events
2024
Case Series
Iatrogenic botulism Cases After Gastric and Axillary Application of Botulinum Toxin and Review of Literature
Case series of six patients who developed iatrogenic botulism following gastric or axillary botulinum toxin injections, with symptoms including blurred vision, dysphagia, muscle weakness, and in some cases respiratory distress requiring intensive care, highlighting risks associated with high doses and unlicensed products.
Mechanism
2023
Animal Study
Presynaptic Entry and Sorting of Botulinum Neurotoxin A Determines Its Toxicity
Experimental study demonstrating that botulinum neurotoxin type A enters neurons via presynaptic endocytosis and is sorted into specific intracellular compartments, including synaptic vesicles and tubular structures, with synaptotagmin-1 playing a critical role in toxin internalization and localization, ultimately determining neuronal intoxication and SNAP-25 cleavage.
Clinical
2018
Human Study
Brain Functional Changes In Patients With Botulism After Illegal Cosmetic Injections Of Botulinum Toxin: A Resting-State fMRI Study
Resting-state fMRI study of patients with botulism following cosmetic botulinum toxin injections demonstrating significant alterations in brain activity, including reduced regional homogeneity and low-frequency fluctuation in cerebellar and parahippocampal regions, indicating that botulinum toxin can directly modulate central nervous system function in humans.
Mechanism
2015
Animal Study
Axonal Transport of Botulinum Toxin A From Periphery to Central Nervous System
Experimental study demonstrating that botulinum toxin type A undergoes axonal retrograde transport from peripheral injection sites to the central nervous system, with evidence of toxin activity in spinal cord neurons, supporting the concept of non-local effects and central nervous system involvement following peripheral administration.
Mechanism of Action
2008
Experimental Study
Long-Distance Retrograde Effects of Botulinum Neurotoxin A
Demonstrates that botulinum toxin type A can undergo long-distance retrograde transport within neurons, reaching central nervous system structures and affecting synaptic activity beyond the injection site. The central nervous system, meaning: the brain and spinal cord.
Mechanism
2024
In Vitro (human neuron-glia model)
Botulinum Neurotoxin Induces Neurotoxic Microglia Mediated by Exogenous Inflammatory Responses
Experimental study using a 3D human neuron–astrocyte–microglia model demonstrating that repeated exposure to botulinum neurotoxin type A induces neuroinflammatory and neurodegenerative processes in the central nervous system. BoNT/A reduces acetylcholine, activates astrocytes, and upregulates complement proteins (C1q, C3, C5), leading to proinflammatory microglial activation. This cascade results in synaptic impairment, phosphorylated tau accumulation, and progressive neuronal loss, suggesting a mechanistic link between BoNT/A exposure and neurodegeneration.
Adverse Events
2023
Survey Study (mixed-methods)
Quantitative and Qualitative Analysis of Individual Experiences Post Botulinum Toxin Injection – United Kingdom Survey
Mixed-method survey of 511 individuals in the UK examining patient-reported outcomes following cosmetic botulinum toxin injections, finding that 79% reported adverse events and 69% reported long-lasting effects, with many individuals describing persistent physical, emotional, and psychological harm.
Mechanism
2021
Review
Botulinum Neurotoxins in Central Nervous System: An Overview From Animal Models to Human Therapy
Comprehensive review examining evidence that botulinum neurotoxins can affect the central nervous system through indirect peripheral mechanisms, retrograde axonal transport, and direct central administration, with data from both animal models and human studies supporting central alterations, neuroplastic changes, and potential therapeutic applications in neurological and neurodegenerative disorders.
Adverse Events
2018
Clinical Study
Clinical Analysis of 86 Botulism Cases Caused by Cosmetic Injection of Botulinum Toxin (BoNT)
Analyzes 86 cases of botulism following cosmetic botulinum toxin injections, documenting widespread neurological and systemic symptoms occurring within days to weeks after exposure.
Adverse Events
2016
Case Report
Impaired Neuronal Communication Syndrome (INCS) as
Novel Neurological Side Effect to Botulinum Toxin Type
A Therapy with 16 Case Reports
Describes a proposed syndrome (INCS) based on 16 patients experiencing widespread neurological, autonomic, and systemic symptoms following botulinum toxin exposure, often without abnormal lab or imaging findings.
Clinical
2013
Case Report
Central Nervous System Toxicity After Botulinum Neurotoxin Injection
Case report of a 62-year-old woman with Parkinson’s disease who developed severe generalized dystonia following repeated botulinum toxin type A injections for hand spasticity. Symptoms included widespread muscle contractures and functional impairment, with no alternative cause identified on imaging or clinical workup. The authors propose that systemic absorption or distant effects of the toxin may contribute to central nervous system involvement, highlighting the potential for neurological effects beyond the injection site.
Full Library
Browse all indexed studies by category and study type
Mechanism of Action
Review
2026
Botulinum Neurotoxins: A Distinct Subclass of SNARE-Cleaving Endopeptidases
Review describing botulinum neurotoxins as a unique class of zinc-dependent endopeptidases that specifically cleave SNARE proteins, thereby blocking acetylcholine release at the neuromuscular junction. This mechanism results in inhibition of synaptic transmission and subsequent flaccid paralysis. The paper emphasizes the highly specialized enzymatic activity underlying botulinum toxin’s potency and its ability to disrupt essential neuronal communication pathways.
Clinical / Diagnosis
Case Series
2025
Comprehensive Analysis of Partial Confounding Clinical Symptoms and Treatment Options of Botulism: A Case Series
Case series of 8 patients with botulism (including iatrogenic cases following cosmetic injections) demonstrating both typical and atypical clinical presentations. Common findings included ptosis, palatal weakness, descending paralysis, and respiratory involvement, while atypical features such as unilateral symptoms, gastrointestinal presentations, and altered consciousness contributed to frequent misdiagnosis and delayed diagnosis. Most patients experienced diagnostic delays exceeding 7 days, and treatment often required respiratory support and prolonged care.
Adverse Events
Case Report
2025
Iatrogenic Botulism Following Botulinum Toxin Injection in Palmar Hyperhidrosis: A Case Report
Case report of a 28-year-old woman who developed progressive neurological symptoms including ptosis, dysphagia, diplopia, and generalized weakness two weeks after botulinum toxin injections for palmar hyperhidrosis, initially mimicking myasthenia gravis and requiring medical management.
Adverse Events / Clinical
Case Report
2025
A Hospitalist’s Challenge: Systemic Botulism Following a Cosmetic Injection Requiring Antitoxin Therapy and Percutaneous Endoscopic Gastrostomy (PEG)
Case report of systemic botulism following cosmetic botulinum toxin injections, presenting with progressive dysphagia, bilateral ptosis, facial weakness, and generalized neuromuscular dysfunction. The patient required botulinum antitoxin therapy and PEG tube placement for nutritional support due to prolonged bulbar impairment. Findings highlight the risk of systemic toxicity after cosmetic use.
Mechanism / Clinical
Case Report
2024
Electrophysiological Abnormalities of Neuromuscular Transmission in Two Patients With Botulism-Like Syndrome Following Botulinum-A Muscle Injections
Case report of two patients who developed systemic botulism-like symptoms following intramuscular botulinum toxin injections, with electrophysiological evidence of impaired neuromuscular transmission. Both patients demonstrated a progressive decrement on low-frequency repetitive nerve stimulation (RNS) in muscles distant from the injection site, supporting systemic toxin spread. Symptoms included generalized weakness, fatigability, and dyspnea, with onset within 1–2 weeks and eventual recovery over several months. Findings highlight that objective neuromuscular abnormalities can occur even without classic cranial nerve symptoms and provide diagnostic markers for iatrogenic botulism.
Adverse Events
Case Report
2024
From Beauty to Botulism: A Case Report Highlighting the Rare Risk of Botox Administration
Case report of a 47-year-old female who developed progressive neurological symptoms including ptosis, dysphagia, hoarseness, and weakness following cosmetic botulinum toxin injections abroad, with clinical deterioration prior to treatment and rapid improvement after antitoxin administration, highlighting diagnostic challenges and systemic toxicity risk.
Adverse Events
Case Series
2024
Iatrogenic botulism Cases After Gastric and Axillary Application of Botulinum Toxin and Review of Literature
Case series of six patients who developed iatrogenic botulism following gastric or axillary botulinum toxin injections, with symptoms including blurred vision, dysphagia, muscle weakness, and in some cases respiratory distress requiring intensive care, highlighting risks associated with high doses and unlicensed products.
Mechanism / Clinical Overview
Clinical Reference / Review
2023
Botulism Antitoxin
Comprehensive clinical overview of botulinum toxin describing its mechanism of action, pharmacology, clinical uses, and potential adverse effects. Botulinum toxin inhibits acetylcholine release at the neuromuscular junction, leading to localized paralysis, but may also produce systemic effects through diffusion or unintended spread. Reported adverse effects include dysphagia, generalized weakness, respiratory compromise, and autonomic symptoms, particularly at higher doses or in susceptible individuals.
Adverse Events
Case Series
2023
Transient Worsening of Dysphagia and Dysarthria after Treatment with Botulinum Toxin in Patients with Acquired Brain Injury
This case series describes three patients with severe acquired brain injury who experienced worsening dysphagia (swallowing difficulty) and dysarthria (speech impairment) following botulinum toxin treatment for spasticity. Symptoms declined within one week post-injection and required intensive speech therapy for recovery. All patients returned to baseline within approximately 3 weeks. The findings highlight that botulinum toxin may contribute to transient systemic or functional adverse effects, particularly involving swallowing and speech, even when used therapeutically.
Adverse Event
Case Report
2023
Case Series + Review
Case report of a 35-year-old woman who developed ischemic skin changes in the central forehead following cosmetic botulinum toxin injection to the glabella. Symptoms began within 72 hours and included livedoid discoloration and tenderness in the supratrochlear region. The authors propose a rare vascular occlusion mechanism, potentially related to needle micro-coring or embolic debris rather than the toxin itself. The lesion resolved with supportive treatment, highlighting a rare but possible vascular complication associated with injection procedures.
Clinical / Diagnosis
Case Report
2022
The Key Role of the Ophthalmologist in Diagnosing Botulism: Two Case Reports
Case report of two patients presenting with early ophthalmic manifestations of botulism, including blurred vision, diplopia, accommodation palsy, and mydriasis, followed by progression to dysphagia, dysarthria, and systemic symptoms. Diagnosis was initially challenging due to overlapping neurological conditions, but both patients improved following administration of botulinum antitoxin. Findings emphasize the importance of early clinical recognition—particularly the “four Ds” (diplopia, dysphagia, dysarthria, dry mouth)—and highlight the risk of delayed diagnosis in botulism cases.
Adverse Events
Animal Study
2021
Botulinum Toxin in the Masseter Muscle: Lingering Effects of Denervation
Experimental study demonstrating that botulinum toxin type A injections into the masseter muscle result in significant mandibular bone loss due to reduced muscle activity and mechanical loading. The study showed decreased bone density and structural deterioration of the mandible, supporting that repeated or localized muscle paralysis can lead to progressive skeletal changes.
Adverse Events
Animal Study
2019
Mandibular Bone Loss After Botulinum Toxin Type A Injection in Masticatory Muscles
Experimental study demonstrating that botulinum toxin type A injections into masticatory muscles result in significant mandibular bone loss due to reduced mechanical loading. The study showed decreased bone volume, trabecular thickness, and overall bone quality, highlighting that muscle paralysis induced by BoNT/A can lead to structural skeletal changes and long-term musculoskeletal consequences.
Mechanism
Review (preclinical + clinical evidence)
2018
Direct Central Nervous System Effects of Botulinum Neurotoxin
Review of experimental and clinical evidence demonstrating that botulinum neurotoxin type A undergoes retrograde axonal transport into the central nervous system, with subsequent transsynaptic spread and measurable functional effects beyond the peripheral injection site, challenging the assumption that its action is purely local.
Clinical
Case Report
2018
Bulbar Muscle Weakness in the Setting of Therapeutic Botulinum Injections
Case report of a 16-year-old patient who developed progressive bulbar muscle weakness, including choking and difficulty managing secretions, following repeated therapeutic botulinum toxin injections for spasticity. Symptoms fluctuated over time and correlated with dosing, improving after dose reduction, supporting systemic effects of the toxin beyond the injection site.
Adverse Events
Case Report
2017
Vitreous Hemorrhage and Rhegmatogenous Retinal Detachment That Developed After Botulinum Toxin Injection to the Extraocular Muscle: Case Report
Case report of a 34-year-old woman who developed sudden vision loss, vitreous hemorrhage, and rhegmatogenous retinal detachment within days after botulinum toxin injection into the extraocular muscle. Imaging confirmed retinal tear and subretinal fluid, with progression requiring surgical intervention including vitrectomy and laser photocoagulation. The case highlights the potential for severe ocular complications following injection, emphasizing the need for prompt evaluation when visual symptoms occur.
Adverse Events
Case Report
2016
Rapidly Progressive Muscle Paralysis and Acute Respiratory Failure Following Endoscopic Botulinum Toxin Injection
Case report of a 90-year-old female who developed rapidly progressive muscle paralysis within hours of endoscopic botulinum toxin injection for achalasia, progressing to diaphragmatic involvement and respiratory failure requiring prolonged mechanical ventilation, ultimately resulting in death after a 4-month ICU course, highlighting the potential for catastrophic systemic toxicity even at therapeutic doses.
Mechanism
Animal Study
2015
Axonal Transport of Botulinum Toxin A From Periphery to Central Nervous System
Experimental study demonstrating that botulinum toxin type A undergoes axonal retrograde transport from peripheral injection sites to the central nervous system, with evidence of toxin activity in spinal cord neurons, supporting the concept of non-local effects and central nervous system involvement following peripheral administration.
Mechanism of Action
Experimental Study
2014
Acrylamide Inhibits Nerve Sprouting Induced by Botulinum Toxin Type A
Investigates how nerve sprouting contributes to recovery after botulinum toxin exposure and shows that acrylamide can inhibit this process, delaying neuromuscular recovery and reducing nerve fiber regeneration.
Mechanism
Animal Study
2012
Botulinum Neurotoxin A Impairs Neurotransmission Following Retrograde Transynaptic Transport
Experimental study in rats demonstrating that botulinum toxin A undergoes retrograde axonal transport and transsynaptic spread, reaching neurons at least two synapses away from the injection site, where it cleaves SNAP-25 and causes structural and functional impairments in neurotransmission, including enlarged synaptic terminals, vesicle accumulation, and reduced cholinergic activity.
Clinical
Case Series + Review
2010
Systemic Weakness After Therapeutic Injections of Botulinum Toxin A: A Case Series and Review of the Literature
Case series and literature review describing systemic effects of botulinum toxin type A characterized by generalized muscle weakness distant from injection sites. The paper presents three patients who developed widespread weakness, dysphagia, gait instability, and functional decline following therapeutic injections, despite prior tolerance of similar doses. Electrophysiological findings confirmed denervation in non-injected muscles, supporting systemic spread. The review suggests that total dose and injection frequency may contribute to risk, with repeated high-dose injections increasing the likelihood of systemic toxicity.
Mechanism of Action
Experimental Study
2008
Long-Distance Retrograde Effects of Botulinum Neurotoxin A
Demonstrates that botulinum toxin type A can undergo long-distance retrograde transport within neurons, reaching central nervous system structures and affecting synaptic activity beyond the injection site. The central nervous system, meaning: the brain and spinal cord.
Clincal Study
Experimental Study
1992
Botulinum Toxin Therapy: Distant Effects on Neuromuscular Transmission and Autonomic Nervous System
Evaluates distant effects of botulinum toxin in five patients using electromyography and autonomic testing, showing measurable changes in neuromuscular transmission and mild abnormalities in cardiovascular autonomic function beyond the injection site.
Adverse Events / Clinical
Prospective Observational Study
2026
Post-Botulinum Headache in Cosmetic Practice: A Prospective Study
Prospective study of 102 patients receiving cosmetic botulinum toxin injections found post-procedural headache in 12.7% of cases. Headaches were typically mild-to-moderate, short-lived (1–2 days), and self-limited, occurring most frequently in first-time recipients and following upper facial injections. No association was found with toxin dose, procedural pain, or systemic comorbidities. Findings suggest post-injection headache is a relatively common but generally transient adverse effect in cosmetic practice.
Adverse Events / Clinical
Case Report
2025
Iatrogenic Botulism Following Unregulated Cosmetic Botulinum Toxin Injection
Case report of iatrogenic botulism following unlicensed cosmetic botulinum toxin injections administered outside a medical setting. The patient developed progressive cranial nerve dysfunction, including ptosis, dysphagia, dysphonia, and autonomic symptoms, while a second exposed individual required intensive care and mechanical ventilation.
Adverse Events / Epidemiology
Outbreak Investigation / Case-Control Study
2025
A Local Outbreak of Iatrogenic Botulism Associated with Cosmetic Injections of Botulinum Neurotoxin-Containing Products, England, 2025
Outbreak investigation identifying 25 cases of iatrogenic botulism following cosmetic botulinum toxin injections in England. Most patients developed symptoms within days, including dysphagia, ptosis, fatigue, and generalized weakness, with 64% requiring antitoxin and hospital admission. Cases were strongly associated with unlicensed products and specific practitioners, and testing revealed toxin potency significantly higher than labeled.
Adverse Events
Cross-Sectional Survey Study
2025
Findings From the Great British and Northern Ireland Botulinum Toxin Survey: Treatment Outcomes, Patient Experience, and Regulations From a Cross-Sectional Survey
A national cross-sectional survey of 919 individuals receiving cosmetic botulinum toxin injections, identifying both acute and long-term complications, gaps in informed consent, and significant variability in practitioner qualifications, highlighting real-world safety concerns and underreporting of adverse events.
Adverse Events
Case Report
2024
From Botox Party to Botulism: A Case Report and Public Health Warning on Adulterated Botulinum Toxin Injection
Case report of a 59-year-old female who developed bulbar paralysis, dysphagia, ptosis, and respiratory symptoms following cosmetic botulinum toxin injections administered by an unlicensed individual at a home “Botox party,” with rapid improvement after antitoxin, highlighting risks of counterfeit products and non-medical administration.
Adverse Events
Case Series
2024
Iatrogenic botulism after botulinum toxin type A: Five cases
Case series of five patients who developed systemic botulism symptoms including ptosis, dysphagia, respiratory difficulty, and generalized muscle weakness following botulinum toxin injections for cosmetic, hyperhidrosis, and obesity indications, with several cases requiring antitoxin and demonstrating dose-related severity.
Adverse Events
Observational Study (pharmacovigilance study)
2024
Real-Life Prognosis of Neurological Complications after Botulinum Toxin Injection
A nationwide pharmacovigilance study analyzing neurological complications following botulinum toxin injections, finding that over half of adverse reactions were initially serious, with symptoms consistent with botulism spectrum effects, occurring both locally and distant from the injection site.
Adverse Events
Case Report
2023
Iatrogenic botulism – A Possible Cause of Generalised Muscular Weakness in Child
Case report of a 5-year-old child with cerebral palsy who developed generalized muscular weakness, ptosis, dysphagia, and speech impairment one week after botulinum toxin injections for spasticity, with symptoms gradually resolving over approximately two months, highlighting systemic toxin spread and prolonged functional impact in a pediatric patient.
Mechanism
Animal Study
2023
Presynaptic Entry and Sorting of Botulinum Neurotoxin A Determines Its Toxicity
Experimental study demonstrating that botulinum neurotoxin type A enters neurons via presynaptic endocytosis and is sorted into specific intracellular compartments, including synaptic vesicles and tubular structures, with synaptotagmin-1 playing a critical role in toxin internalization and localization, ultimately determining neuronal intoxication and SNAP-25 cleavage.
Mechanism / Clinical Overview
Clinical Reference / Review
2023
Botulinum Toxin (Botulism) Factsheet
Clinical factsheet describing botulinum toxin as one of the most potent neurotoxins known, causing flaccid paralysis through inhibition of acetylcholine release. Symptoms typically begin with cranial nerve dysfunction (blurred vision, dysphagia, dysarthria) and progress to descending paralysis, potentially leading to respiratory failure and death. Diagnosis is primarily clinical and often delayed, with recovery requiring regeneration of nerve endings over weeks to months, and in some cases, long-term fatigue and respiratory issues may persist.
Mechanism of Action
In Vitro
2021
Botulinum Neurotoxin Inhibitor Binding Dynamics and Kinetics
Relevant for Drug Design
Expands on prior work examining how compounds bind to the botulinum toxin light chain, identifying additional inhibitors and refining understanding of how its enzymatic activity may be disrupted.
Adverse Events
Case Series
2020
Morphea-Like Lesions After Botulinum Toxin A Injections
Case series describing three patients who developed localized atrophic, morphea-like skin lesions following cosmetic botulinum toxin type A injections. Lesions appeared within weeks of treatment and presented as circular depressions in the forehead. Histologic evaluation in one case ruled out true morphea, and lesions resolved over time. Authors propose potential mechanisms including focal neurogenic muscle atrophy or reaction to syringe lubricant contamination, highlighting a previously underreported cutaneous adverse effect of BoNT/A.
Clinical
Case Report
2019
Rare Complication of Botox Injection: A Case Report
Case report of a 22-year-old male who developed generalized botulinum toxin complications following axillary hyperhidrosis treatment after receiving an excessive dose. Symptoms included fatigue, generalized muscle weakness, dysphagia, diplopia, and ptosis, consistent with systemic spread of the toxin. Symptoms improved with pyridostigmine treatment, highlighting the potential for dose-related systemic and autonomic effects even in cosmetic or therapeutic use.
Clinical
Human Study
2018
Brain Functional Changes In Patients With Botulism After Illegal Cosmetic Injections Of Botulinum Toxin: A Resting-State fMRI Study
Resting-state fMRI study of patients with botulism following cosmetic botulinum toxin injections demonstrating significant alterations in brain activity, including reduced regional homogeneity and low-frequency fluctuation in cerebellar and parahippocampal regions, indicating that botulinum toxin can directly modulate central nervous system function in humans.
Adverse Effects
Review (perspective/narrative review)
2018
Mandibular Bone Loss: A Hidden Side Effect of Botulinum Toxin Type A Injection in Masticatory Muscles
Reviews evidence suggesting that botulinum toxin injections in masticatory muscles may lead to mandibular bone loss through muscle atrophy and reduced mechanical loading, with supporting findings from animal models and limited human imaging studies.
Adverse Events
Animal Study
2017
Injection of High Dose Botulinum Toxin A Leads to Impaired Skeletal Muscle Function and Damage of the Fibrillar and Non-Fibrillar Structures
Experimental study demonstrating that high-dose intramuscular botulinum toxin type A injections cause significant structural and functional damage to skeletal muscle. Findings included a reduction in fibrillar tissue, increase in non-fibrillar tissue, loss of normal muscle architecture, and significant muscle atrophy (~45% decrease in muscle mass). Functional impairments such as altered gait and reduced strength were observed, along with gene expression changes indicating inflammation, remodeling, and muscle degeneration.
Adverse Events
Case Report
2016
Impaired Neuronal Communication Syndrome (INCS) as
Novel Neurological Side Effect to Botulinum Toxin Type
A Therapy with 16 Case Reports
Describes a proposed syndrome (INCS) based on 16 patients experiencing widespread neurological, autonomic, and systemic symptoms following botulinum toxin exposure, often without abnormal lab or imaging findings.
Adverse Events
Case Series
2016
Frontal Alopecia after Repeated Botulinum Toxin Type A Injections for Forehead Wrinkles: An Underestimated Entity?
Reports five cases of progressive frontal hairline recession following repeated botulinum toxin injections, with evidence of hair follicle miniaturization and no scarring, suggesting a previously underrecognized form of toxin-associated alopecia.
Mechanism
Human Study
2015
Regional Diffusion of Botulinum Toxin in Facial Muscles: A Randomised Double-Blind Study and a Consideration for Clinical Studies with Split-Face Design
Randomized, double-blind human study demonstrating that botulinum toxin type A injected unilaterally into facial muscles diffuses to both adjacent and contralateral muscles. Neurophysiological measurements showed reduced muscle activity (CMAP decrease) not only at the injection site but also in untreated contralateral muscles, along with increased jitter indicating impaired neuromuscular transmission. Findings confirm regional diffusion and challenge the validity of split-face study designs that assume localized effects.
Clinical
Case Report
2013
Central Nervous System Toxicity After Botulinum Neurotoxin Injection
Case report of a 62-year-old woman with Parkinson’s disease who developed severe generalized dystonia following repeated botulinum toxin type A injections for hand spasticity. Symptoms included widespread muscle contractures and functional impairment, with no alternative cause identified on imaging or clinical workup. The authors propose that systemic absorption or distant effects of the toxin may contribute to central nervous system involvement, highlighting the potential for neurological effects beyond the injection site.
Mechanism
Experimental (in vitro neuronal study)
2012
Tetanus Toxin and Botulinum Toxin A Utilize Unique Mechanisms To Enter Neurons of the Central Nervous System
Experimental study demonstrating that botulinum toxin type A and tetanus toxin enter neurons through distinct cellular mechanisms. Botulinum toxin A relies on synaptic vesicle cycling and SV2 receptor binding, while tetanus toxin can enter neurons independently of synaptic vesicle cycling and does not bind SV2. The findings support multiple neuronal entry pathways, including calcium-independent and endosome-mediated mechanisms, highlighting the complexity of toxin trafficking within the central nervous system.
Mechanism of Action
Review
2010
Bacterial Toxins and the Nervous System: Neurotoxins and
Multipotential Toxins Interacting with Neuronal Cells
Provides an overview of botulinum neurotoxin structure and function, detailing how the toxin enters nerve terminals, cleaves SNARE proteins, and blocks acetylcholine release, leading to neuromuscular paralysis.
Adverse Events
Case Series
2006
Botulism in 4 Adults Following Cosmetic Injections with an Unlicensed, Highly Concentrated Botulinum Preparation
Case series of four adults who developed systemic botulism after receiving cosmetic botulinum toxin injections from an unlicensed, highly concentrated preparation, presenting with cranial nerve dysfunction and descending paralysis, prompting a public health investigation and highlighting risks associated with product variability and improper administration.
Clinical / Outcomes
Systematic Review
2025
Botulism Sequelae: A Systematic Review
Systematic review of post-botulism outcomes showing persistent long-term symptoms in survivors, including fatigue, generalized weakness, dyspnea, and reduced physical capacity. Psychosocial dysfunction may persist for years, even after physical recovery. Findings indicate that botulism can result in prolonged neuromuscular and autonomic impairment with measurable impact on quality of life.
Adverse Events
Case Series
2025
Dysphagia and Muscle Weakness Caused by Botulinum Toxin Poisoning after Cosmetic Injection: Three Case Reports and Clinical Warnings
Case series of three patients who developed dysphagia, dysarthria, and generalized muscle weakness following cosmetic botulinum toxin injections, with symptoms occurring days to weeks after treatment, highlighting risks of toxin diffusion and systemic effects.
Adverse Events
Case Report
2025
Iatrogenic Botulism Following Cosmetic Botulinum Toxin Injection Presenting With Respiratory Distress: A Case Report
Case report of a previously healthy 47-year-old male who developed progressive neurological symptoms, including ptosis, dysphagia, and respiratory failure requiring mechanical ventilation, following cosmetic botulinum toxin injection, highlighting the potential for severe systemic toxicity even with routine aesthetic use.
Adverse Events
Observational Study
2025
Analysis of Clinical Challenges and Prognostic Risk Factors for 195 Cases of Iatrogenic Botulism
Analysis of 195 cases of iatrogenic botulism identifying common early neurological symptoms, including blurred vision, ptosis, fatigue, and dysarthria, along with complications such as aspiration pneumonia, highlighting real-world risks associated with botulinum toxin exposure.
Mechanism
In Vitro (human neuron-glia model)
2024
Botulinum Neurotoxin Induces Neurotoxic Microglia Mediated by Exogenous Inflammatory Responses
Experimental study using a 3D human neuron–astrocyte–microglia model demonstrating that repeated exposure to botulinum neurotoxin type A induces neuroinflammatory and neurodegenerative processes in the central nervous system. BoNT/A reduces acetylcholine, activates astrocytes, and upregulates complement proteins (C1q, C3, C5), leading to proinflammatory microglial activation. This cascade results in synaptic impairment, phosphorylated tau accumulation, and progressive neuronal loss, suggesting a mechanistic link between BoNT/A exposure and neurodegeneration.
Adverse Events
Case Study
2024
Iatrogenic Botulism
Case report of a woman in her forties who developed progressive neurological symptoms, including ptosis, dysphagia, and neck muscle weakness, following botulinum toxin injections received abroad, with prolonged recovery and persistent functional impairment months after exposure.
Adverse Events
Survey Study (mixed-methods)
2023
Quantitative and Qualitative Analysis of Individual Experiences Post Botulinum Toxin Injection – United Kingdom Survey
Mixed-method survey of 511 individuals in the UK examining patient-reported outcomes following cosmetic botulinum toxin injections, finding that 79% reported adverse events and 69% reported long-lasting effects, with many individuals describing persistent physical, emotional, and psychological harm.
Adverse Events / Epidemiology
Editorial / Outbreak Analysis
2023
Lessons from a Recent Multicountry Iatrogenic Botulism Outbreak
Editorial analysis of a large multicountry iatrogenic botulism outbreak in Europe associated with intragastric botulinum toxin injections for weight loss, involving at least 87 reported cases across multiple countries. The report highlights systemic symptoms consistent with botulism (including dysphagia, ptosis, and generalized weakness), links cases to off-label and unregulated use, and emphasizes underreporting, diagnostic challenges, and the need for improved surveillance and clinical awareness.
Regulatory / Safety
Policy / Petition
2023
Public Citizen Petition to the FDA Regarding Botulinum Toxin Safety Concerns
Formal petition submitted to the FDA raising concerns about the safety profile of botulinum toxin products, including risks of systemic spread, adverse events, and insufficient patient warning. The document highlights gaps in risk communication, underreporting of complications, and the need for stronger regulatory oversight and labeling to better reflect potential serious outcomes associated with botulinum toxin use.
Adverse Events
Systematic Review and Meta-Analysis
2022
Complications of Cosmetic Botulinum Toxin A Injections to the Upper Face: A Systematic Review and Meta-Analysis
Systematic review and meta-analysis of 24 studies (over 4,000 injection sessions) evaluating complications from cosmetic botulinum toxin use in the upper face, finding an overall complication rate of approximately 16%, with common effects including headache, local skin reactions, and neuromuscular symptoms.
Mechanism
Review
2021
Botulinum Neurotoxins in Central Nervous System: An Overview From Animal Models to Human Therapy
Comprehensive review examining evidence that botulinum neurotoxins can affect the central nervous system through indirect peripheral mechanisms, retrograde axonal transport, and direct central administration, with data from both animal models and human studies supporting central alterations, neuroplastic changes, and potential therapeutic applications in neurological and neurodegenerative disorders.
Review
Literature Review
2020
A Review on Iatrogenic Botulism
This review examines iatrogenic botulism following cosmetic and therapeutic use of botulinum toxin. The toxin blocks cholinergic transmission at the neuromuscular junction and can spread beyond the injection site to adjacent or distant structures. Common symptoms include weakness, dysphagia, ptosis, and blurred vision. Around 20% of reported cases required antitoxin treatment. The paper emphasizes the importance of proper dosing, administration technique, and clinical awareness to reduce risk.
Adverse Events / Clinical
Case Report + Literature Review
2019
Cosmetic Injection of Botulinum Toxin Unmasking Subclinical Myasthenia Gravis: A Case Report and Literature Review
Case report describing a patient who developed progressive ocular and systemic neuromuscular symptoms following cosmetic botulinum toxin injection, ultimately revealing previously undiagnosed (subclinical) myasthenia gravis. The combined presynaptic effects of botulinum toxin and postsynaptic impairment from myasthenia gravis produced a synergistic disruption of neuromuscular transmission, resulting in dysphagia, generalized weakness, and prolonged symptoms. Findings highlight increased susceptibility to adverse effects in individuals with underlying or unrecognized neuromuscular disorders.
Adverse Events
Clinical Study
2018
Clinical Analysis of 86 Botulism Cases Caused by Cosmetic Injection of Botulinum Toxin (BoNT)
Analyzes 86 cases of botulism following cosmetic botulinum toxin injections, documenting widespread neurological and systemic symptoms occurring within days to weeks after exposure.
Mechanism
Review
2017
Neurophysiological Measures of Efficacy and Safety for Botulinum Toxin Injection in Facial and Bulbar Muscles: Special Considerations
Review examining neurophysiological measures of botulinum toxin effects and safety, highlighting that toxin diffusion beyond the injection site can lead to unintended effects in adjacent and distant muscles. The paper discusses dose-dependent complications such as dysphagia and generalized muscle weakness, as well as evidence of retrograde transport and spread to non-targeted muscles, emphasizing the importance of accurate dosing, injection technique, and monitoring for systemic and neurological effects.
Mechanism / Review
Literature Review
2016
Botulinum Toxin and Its Biological Significance: A Review
Comprehensive review of botulinum toxin describing its biological activity, mechanism of action, and systemic effects across humans and animals. Botulinum toxin acts as a zinc-dependent endopeptidase that blocks acetylcholine release at the neuromuscular junction, resulting in flaccid paralysis. Clinical manifestations include generalized weakness, dysphagia, and progressive paralysis that can lead to respiratory failure and death. The toxin is noted for its extreme potency and ability to affect multiple species, with systemic distribution following absorption.
Mechanism
Animal Study
2016
Interneuronal Transfer of Botulinum Neurotoxin A After Peripheral Injection
Experimental study demonstrating that botulinum neurotoxin type A can undergo interneuronal transfer following peripheral injection, moving from primary motor neurons to connected neurons within the central nervous system. The study confirmed cleaved SNAP-25 in second-order neurons, providing direct evidence of transsynaptic spread and functional toxin activity beyond the initial injection site.
Adverse Events
Prospective Observational Study
2015
Questionnaire About The Adverse Events and Side Effects Following Botulinum Toxin A Treatment in Patients with Cerebral Palsy
A prospective study using active surveillance via patient and caregiver questionnaires to capture adverse events following botulinum toxin treatment, finding that over half of treatments were associated with reported side effects, including generalized weakness, fatigue, and distant effects, suggesting adverse events may be underreported in standard clinical monitoring.
Mechanism
Animal Study
2012
Transynaptic Inhibition of Motoneurons by Botulinum Neurotoxin A
Experimental animal study demonstrating that botulinum neurotoxin type A can produce transynaptic inhibition of motoneurons, indicating central nervous system effects beyond the injection site and supporting evidence of retrograde transport and functional changes within neural circuits.
Mechanism
Review
2010
Botulinum Toxin
Comprehensive review describing the pharmacology, mechanism of action, and clinical applications of botulinum toxin. The paper explains how botulinum toxin inhibits acetylcholine release at cholinergic nerve terminals, leading to muscle paralysis, and highlights its effects at the neuromuscular junction, autonomic ganglia, and postganglionic nerve endings. It also discusses clinical uses, duration of action, antibody formation, and potential adverse effects, including toxin diffusion and rare systemic spread.
Mechanism
Review
1996
Critical Aspects of Bacterial Protein Toxins
Review of the structural and functional properties of bacterial protein toxins, including botulinum neurotoxins, highlighting their mechanisms of cellular entry, intracellular trafficking, and enzymatic activity. The paper outlines how these toxins exploit receptor-mediated endocytosis and intracellular transport pathways to disrupt host cellular processes, providing foundational insight into neurotoxin behavior and toxicity.