Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Botox (Onabotulinumtoxin-a). If you are concerned about side effects, discuss the risks and benefits of Botox (Onabotulinumtoxin-a) with your doctor.

The following side effects have been reported by at least 1% of people taking Botox (Onabotulinumtoxin-a). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

General side effects:

• pain, tenderness, or bruising at the place of injection

When used for blepharospasm:

• drooping of the upper eyelid
• double vision
• dry eye
• irritation or watering of the eye
• not able to close the eye completely
• sensitivity of the eye to light
• swelling of the eyelid

When used for cervical dystonia:

• flu symptoms
• local or general weakness
• nausea
• neck weakness

When used for focal spasticity:

• decreased coordination
• feeling of "pins and needles"
• Fever
• flu symptoms
• headache
• increased sensitivity to touch
• itching
• joint pain
• muscle tightness or weakness
• nausea
• pain in the affected limb (arm or leg)

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• difficult or painful swallowing, dizziness, shortness of breath, or vision changes (when used for cervical dystonia)
• facial paralysis or persistent eye irritation or pain (when used for eye conditions)
• falling (when used for spasticity due to cerebral palsy)
• fever, especially when accompanied by coughing and shortness of breath
• irregular heartbeat
• shortness of breath
• skin rash
• symptoms of a urinary tract infection (e.g. pain when urinating, urinating more often than usual, low back or flank pain)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• breathing problems
• difficulty swallowing
• muscle weakness
• peeling or blistering skin
• seizures
• signs of an allergic reaction (e.g., Hives; difficulty breathing; swelling of the mouth, tongue, or throat)
• signs of a Heart Attack (e.g., chest pain or pressure; shortness of breath; jaw, shoulder, or arm pain; nausea; lightheadedness; sweating)
• speech problems

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are using Botox (Onabotulinumtoxin-a).

This product is available in sterile vials containing 50, 100, or 200 Allergan units of Clostridium botulinum toxin type A. Nonmedicinal ingredients: human serum Albumin and sodium chloride. This product contains no preservative.

Do not take botulinum toxin if you:

• are sensitive or allergic to botulinum toxin or to any of the ingredients of Botox (Onabotulinumtoxin-a)
• have an infection at the site the injection is to be given
• have Myasthenia Gravis, amyotrophic lateral sclerosis, or Eaton Lambert syndrome

There may be an interaction between botulinum toxin type A and any of the following:

• aclidinium
• aminoglycoside antibiotics (e.g., gentamicin, neomycin, tobramycin, streptomycin)
• antihistamines (e.g., brompheniramine, Diphenhydramine)
• antipsychotics (e.g. Clozapine, Olanzapine, Risperidone)
• atropine
• azelastine
• belladonna
• Benztropine
• clidinium
• darifenacinflavoxate
• glycopyrrolate
• ipratropium
• muscle relaxants (e.g., Cyclobenzaprine, orphenadrine)
• Oxybutynin
• polymyxins (e.g., polymyxin B)
• quinidine
• scopolamine
• Solifenacin
• tiotropium
• Tolterodine
• tricyclic antidepressants (e.g., Amitriptyline, Clomipramine, Imipramine)
• Trospium
• umeclidinium

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. In many cases, interactions are intended or are managed by close monitoring. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Botox (Onabotulinumtoxin-a). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Botox (Onabotulinumtoxin-a).

Angle-closure Glaucoma: Botulinum toxin can cause angle-closure glaucoma in those at risk. Your doctor will monitor for this if necessary. If you have glaucoma, discuss with your doctor how Botox (Onabotulinumtoxin-a) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Botox (Onabotulinumtoxin-a), and whether any special monitoring is needed.

Distant toxin spread: Very rarely, Botox (Onabotulinumtoxin-a) may spread to other parts of the body other than where it was injected, leading to muscle weakness, difficulty swallowing, pneumonia, speech difficulties, and breathing problems. Distant toxin spread can be fatal. If you develop severe difficulty swallowing, speaking, or breathing while using Botox (Onabotulinumtoxin-a), contact your doctor immediately.

Heart disease: Botulinum toxin has rarely been reported to cause arrhythmia and heart attack. People with heart conditions may be at increased risk of irregular heartbeat or heart attack. If you have a heart condition, discuss with your doctor how Botox (Onabotulinumtoxin-a) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Botox (Onabotulinumtoxin-a), and whether any special monitoring is needed.

Other medical conditions: People with certain nerve or muscle disorders are at increased risk of developing serious side effects, such as difficulty swallowing or breathing. If you have amyotrophic lateral sclerosis, any disorder that produces a depletion of acetylcholine, or disorders that produce peripheral neuromuscular dysfunction, discuss with your doctor how Botox (Onabotulinumtoxin-a) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Botox (Onabotulinumtoxin-a), and whether any special monitoring is needed.

Pregnancy: Botox (Onabotulinumtoxin-a) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while receiving Botox (Onabotulinumtoxin-a), contact your doctor immediately.

Breast-feeding: It is not known if botulinum toxin passes into breast milk. If you are a breast-feeding mother and are receiving Botox (Onabotulinumtoxin-a), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this have not been established for children under 18 years of age.