Skip to main content

OnabotulinumtoxinA Side Effects

Medically reviewed by Philip Thornton, DipPharm. Last updated on Dec 25, 2023.

Applies to onabotulinumtoxinA: powder for solution.


Injection route (Powder for Solution)

Distant spread of toxin effects - The effects of onabotulinumtoxinA and all botulinum toxin products may spread from the area of injection to produce symptoms consistent with botulinum toxin effects. These symptoms have been reported hours to weeks after injection. Swallowing and breathing difficulties can be life threatening and there have been reports of death. The risk of symptoms is probably greatest in children treated for spasticity but symptoms can also occur in adults, particularly in those patients who have an underlying condition that would predispose them to these symptoms.

Serious side effects of OnabotulinumtoxinA

Along with its needed effects, onabotulinumtoxinA may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur while taking onabotulinumtoxinA:

More common


More common—for blepharospasm

More common—for upper limb spasticity

More common—for urinary incontinence caused by an overactive bladder

Less common—for blepharospasm

Less common—for forehead lines

Less common—for glabellar lines

Less common—for lateral canthal lines

Less common—for upper limb spasticity

Other side effects of OnabotulinumtoxinA

Some side effects of onabotulinumtoxinA may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common—for blepharospasm

More common—for cervical dystonia

More common—for chronic migraine

More common—for forehead lines

More common—for hyperhidrosis

More common—for strabismus

More common—for upper limb spasticity

Less common—for blepharospasm

Less common—for chronic migraine

Less common—for forehead lines

Less common—for lower limb spasticity

Less common—for strabismus

For Healthcare Professionals

Applies to onabotulinumtoxinA: injectable powder for injection.


The more commonly reported adverse reactions have included localized pain and headache, otherwise reactions vary based on condition being treated. Local weakness of the injected muscle(s) represents the expected pharmacological action while weakness of nearby muscle may also occur due to spread of toxin.[Ref]


Very common (10% or more): Dysphagia (up to 19%)

Common (1% to 10%): Constipation, nausea

Uncommon (0.1% to 1%): Oral dryness

Frequency not reported: Swallowing difficulties, jaw pain

Postmarketing reports: Abdominal pain, diarrhea, dry mouth, vomiting, anorexia[Ref]

Deaths as a complication of severe dysphagia have been reported with botulinum toxin. In cervical dystonia patients, dysphagia was reported in 19% of patients. Most dysphagia was reported as mild or moderate, however, dyspnea accompanied dysphagia in about 20% of these cases.[Ref]


Very Common (10% or more): Upper respiratory tract infection

Common (1% to 10%): Bronchitis, cough, rhinitis, dyspnea, pharyngitis, rhinorrhea, nasal congestion

Postmarketing reports: Aspiration pneumonia, respiratory depression and or/respiratory failure[Ref]

Patients in the upper limb spasticity trials who had stable, reduced respiratory function at baseline experienced a greater event rate change in forced vital capacity (15% or greater or 20% or greater decline) compared with placebo at weeks 1, 6, and 12. These differences from placebo were not statistically significant, but noticeable. Among patients with restrictive lung disease of neuromuscular aetiology and detrusor overactivity associated with a neurologic condition, the event rate of decreased forced vital capacity (FVC) of 15% or 20% or more was also greater in treated patients compared with placebo. Bronchitis has been reported more frequently in patients treated for upper limb spasticity (3% vs 1%) compared with placebo. In patients with reduced lung function treated for upper limb spasticity, upper respiratory tract infections were reported more frequently in treated patients compared with placebo (up to 11% vs 6%). In patients treated for lower limb spasticity, upper respiratory tract infections were reported more frequently compared with placebo (2% vs 1%). In pediatric patients treated for upper limb spasticity, upper respiratory tract infections were reported more frequently compared with placebo (17% [6 units/kg]; 10% [3 Units/kg]; 9% [placebo]).[Ref]

Nervous system

Common (1% to 10%): Headache, worsening migraine, facial paresis, dizziness, hypertonia, speech disorder, seizures

Uncommon (0.1% to 1%): Vertigo

Frequency not reported: VII nerve disorder

Postmarketing reports: Brachial plexopathy, facial palsy, hypoesthesia, localized numbness, myasthenia gravis, paraesthesia, peripheral neuropathy, radiculopathy, syncope[Ref]


In trials in patients with overactive bladder (OAB), the more commonly reported adverse reactions within the first 12 weeks after intradetrusor injection were urinary tract infection (UTI; 18%), dysuria (9%), urinary retention (6%), bacteriuria (4%) and residual urine volume (3%). A higher incidence of UTI was observed in patients with diabetes than those without (31% vs 26%). The incidence of UTI increased in patients who experienced a maximum post-void residual (PVR) urine volume over 200 mL following injection compared to those whose PVR urine volume was 200 mL or less (44% vs 23%).

Among patients with detrusor overactivity associated with a neurologic condition, urinary tract infection and urinary retention occurred in 24% and 17%, respectively.

Very common (10% or more): Urinary tract infection (up to 26%), urinary retention (up to 17%)

Common (1% to 10%): Dysuria, hematuria, bacteriuria, residual urine volume


Common (1% to 10%): Pain in extremity, muscle weakness, asthenia, back pain, hypertonia, stiffness, fall, gait disturbance, muscle spasm, neck pain, musculoskeletal stiffness, myalgia

Uncommon (0.1% to 1%): Jaw pain

Postmarketing reports: Denervation/muscle atrophy, localized muscle twitching/involuntary muscle contractions, dysarthria,[Ref]


Botulinum Toxin:

Common (1% to 10%): Hypertension

Frequency not reported: Arrhythmia, myocardial infarction (sometimes fatal)[Ref]


Common (1% to 10%): Injection site pain[Ref]


Very common (10% or more): Ptosis (up to 21%)

Common (1% to 10%): Eyelid ptosis, brow ptosis, superficial punctate keratitis, dry eye

Uncommon (0.1% to 1%): Eyelid edema, eye infection, diplopia, retrobulbar hemorrhage

Very rare (less than 0.01%): Corneal perforation

Frequency not reported: Irritation, tearing, lagophthalmos, photophobia, ectropion, keratitis, diplopia, local swelling of the eyelid skin lasting for several days following eyelid injection, reduced blinking (from the injection of the orbicularis muscle which may lead to serious corneal exposure), persistent epithelial defect

Postmarketing reports: Visual disturbance, strabismus, blurred vision[Ref]


Frequency not reported: Anaphylaxis, serum sickness, urticaria, soft tissue edema, dyspnea

A fatal case of anaphylaxis has been reported; in this case, lidocaine was used as the diluent and therefore, the causal agent cannot be determined.


Common (1% to 10%): Fatigue, asthenia, fever,

Frequency not reported: Focal facial paralysis, syncope, exacerbation of myasthenia gravis

Postmarketing reports: Hypoacusis, hypoesthesia, malaise, radiculopathy, tinnitus[Ref]


Common (1% to 10%): Pruritus, skin tightness

Frequency not reported: Diffuse skin rash

Postmarketing reports: Alopecia (including madarosis), hyperhidrosis, pruritus, skin rash, erythema multiforme, dermatitis psoriasiform, psoriasiform eruption[Ref]


Common (1% to 10%): Flu syndrome, infection

Frequency not reported: Immunogenicity (formation of neutralizing antibodies to botulinum toxin type A which may reduce the effectiveness of therapy)[Ref]


Common (1% to 10%): Hemorrhage[Ref]


Common (1% to 10%): Anxiety[Ref]

Frequently asked questions


1. Product Information. Botox (onabotulinumtoxinA). Allergan Inc. PROD.

2. Product Information. Botox Cosmetic (onabotulinumtoxinA). Allergan Inc. 2022.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.