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Botox Side Effects

Generic name: onabotulinumtoxinA

Medically reviewed by Philip Thornton, DipPharm. Last updated on May 31, 2023.

Note: This document contains side effect information about onabotulinumtoxinA. Some dosage forms listed on this page may not apply to the brand name Botox.


Common side effects of Botox include: antibody development. Continue reading for a comprehensive list of adverse effects.

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 Botox

Along with its needed effects, onabotulinumtoxinA (the active ingredient contained in Botox) 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

  • Difficulty with swallowing


  • Difficulty with breathing or speaking
  • muscle weakness

More common—for blepharospasm

  • Dryness of the eyes
  • inability to close the eyelids completely

More common—for upper limb spasticity

  • Body aches or pain
  • chills
  • cough
  • ear congestion
  • fever
  • headache
  • loss of voice
  • runny or stuffy nose
  • sneezing
  • sore throat
  • unusual tiredness or weakness

More common—for urinary incontinence caused by an overactive bladder

  • Bladder pain
  • bloody or cloudy urine
  • difficult, burning, or painful urination
  • frequent urge to urinate
  • lower back or side pain

Less common—for blepharospasm

  • Decreased blinking
  • irritation of the cornea (colored portion) of the eyes
  • turning outward or inward of the edge of the eyelids

Less common—for forehead lines

  • Drooping of the brows and upper eyelids

Less common—for glabellar lines

  • Drooping of the upper eyelid
  • facial pain
  • muscle weakness
  • partial or slight paralysis of the face

Less common—for lateral canthal lines

  • Swelling of the eyelids

Less common—for upper limb spasticity

  • Cough producing mucus
  • difficulty breathing
  • muscle weakness
  • nausea
  • seizures
  • tightness in the chest
  • weakness

Other side effects of Botox

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

  • Blue or purplish bruise on the eyelids
  • drooping of the upper eyelids
  • irritation or watering of the eyes
  • sensitivity of the eyes to light

More common—for cervical dystonia

  • Body aches or pain
  • chills
  • cough
  • ear congestion
  • fever
  • headache
  • loss of voice
  • neck pain
  • runny or stuffy nose
  • sneezing
  • sore throat
  • unusual tiredness or weakness

More common—for chronic migraine

  • Neck pain

More common—for forehead lines

  • Headache

More common—for hyperhidrosis

  • Body aches or pain
  • chills
  • congestion
  • cough
  • diarrhea
  • dryness or soreness of the throat
  • fear
  • fever
  • general feeling of discomfort or illness
  • headache
  • heavy bleeding from the place where the shot was given
  • itching skin
  • joint pain
  • loss of appetite
  • nausea
  • nervousness
  • painful or difficult urination
  • runny nose
  • shivering
  • sweating
  • tender, swollen glands in the neck
  • trouble sleeping
  • trouble swallowing
  • voice changes
  • vomiting

More common—for strabismus

  • Drooping of the upper eyelid
  • eye pointing upward or downward instead of straight ahead

More common—for upper limb spasticity

  • Pain in the arms

Less common—for blepharospasm

  • Skin rash
  • swelling of the skin of the eyelid

Less common—for chronic migraine

  • Bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
  • blurred vision
  • body aches or pain
  • cough producing mucus
  • difficulty with breathing
  • dizziness
  • drooping of the upper eyelid
  • headache
  • muscle aches and pains
  • nervousness
  • pounding in the ears
  • slow or fast heartbeat
  • tightness in the chest

Less common—for forehead lines

  • Skin tightness

Less common—for lower limb spasticity

  • Back pain
  • body aches or pain
  • chills
  • cough
  • difficulty with breathing
  • ear congestion
  • fever
  • headache
  • loss of voice
  • sneezing
  • sore throat
  • stuffy nose
  • unusual tiredness or weakness

Less common—for strabismus

  • Difficulty finding the location of objects
  • double vision

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]


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): 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]


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]

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]

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]


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

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.


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]


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.

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


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.

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.