Botox (onabotulinumtoxinA) is a brand-name injection prescribed for various conditions, including overactive bladder, migraine, and excessive sweating. As with other drugs, Botox can cause side effects, which vary depending on the condition being treated.

Botox is a biologic and belongs to the neurotoxin drug class. The drug is not available in a biosimilar version. Botox is a solution that’s available as an intramuscular, intradermal, and intradetrusor injection.*

Read on to learn about potential common, mild, and serious side effects of Botox. For a general overview of the drug, including details about its uses, see this article.

Note: This article focuses on Botox’s medical use, not its cosmetic use. You can see this article for details about cosmetic Botox.

* An intramuscular injection is given into a muscle. An intradermal injection is given into a layer of your skin. And an intradetrusor injection is given into the detrusor, which is the bladder wall.

Botox can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days or weeks. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Botox in clinical trials. These side effects can vary depending on which condition the drug is being used to treat.

More common side effects in people taking Botox for overactive bladder include:

More common side effects in people taking Botox for axillary hyperhidrosis include:

  • excessive sweating in areas other than the underarms
  • sore throat
  • flu-like symptoms, such as fever, chills, headache, or body aches
  • pain or bleeding at the injection site (see “Side effect specifics” below)

More common side effects in people taking Botox for cervical dystonia include:

More common side effects in people taking Botox for strabismus include:

More common side effects in people taking Botox for urinary incontinence caused by a neurological disorder include:

More common side effects in people taking Botox for blepharospasm (uncontrollable blinking) associated with dystonia include:

  • drooping eyelids
  • dry eyes
  • eye inflammation (damage and swelling)

More common side effects in adults taking Botox for spasticity of the bladder include:

  • pain in the extremities, such as hands or feet

More common side effects in children taking Botox for spasticity of the bladder include:

  • upper respiratory tract infection (see “Side effect specifics” below)

More common side effects in people taking Botox for chronic (long-term) migraine include:

  • neck pain
  • headache (see “Side effect specifics” below)

For more information about the conditions that Botox can be used to treat, see this article.

Mild side effects can occur with Botox use. This list doesn’t include all possible mild side effects reported with the drug. For more information, you can refer to Botox’s prescribing information.

It’s important to note that these side effects can vary depending on which condition the drug is being used to treat. For example, someone taking Botox for chronic (long-term) migraine is unlikely to have side effects related to their bladder or ability to urinate.

Mild side effects of Botox can include:

These side effects may be temporary, lasting a few days or weeks. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect while taking Botox and want to tell the FDA about it, visit MedWatch.

* To learn more about this side effect, see the “Side effect specifics” section below.

Botox may cause serious side effects. The list below may not include all possible reported serious side effects of the drug. For more information, you can refer to Botox’s prescribing information.

If you develop serious side effects while taking Botox, call your doctor right away. If the side effects seem life threatening or if you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects and their symptoms can include:

  • Corneal ulceration (an open sore on your cornea, which is the clear covering over the front of your eye).* Symptoms can include:
    • blurry vision
    • feeling that something is in your eye
    • pain and redness in your eye
    • watery eye
    • a white spot on your cornea
  • Problems with breathing or swallowing. Symptoms can include:
    • trouble breathing
    • trouble swallowing
  • Urinary retention.†
  • Spread of toxin effects.†‡
  • Allergic reaction.§

* This side effect occurred when Botox was used to treat blepharospasm, which is uncontrollable blinking.
† To learn more about this side effect, see the “Side effect specifics” section below.
‡ Botox has a boxed warning about the risk of this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effect specifics” section below.
§ An allergic reaction is possible after using Botox. But it’s not clear whether this side effect occurred in clinical trials.

Botox is commonly prescribed to help prevent headaches caused by chronic (long-term) migraine.* More common side effects in people taking Botox for this use in clinical trials included:

Other side effects included neck pain, muscle stiffness, muscle weakness, pain, and redness or discoloration at injection sites.

* Botox has various other approved uses, which are listed in the drug’s prescribing information.

Botox may cause long-term side effects, although this isn’t common. Side effects that may be long term include:

It’s also possible that these or other side effects of Botox may last for a shorter time, such as a few days or weeks.

If you have questions or concerns about how long side effects of Botox may last, talk with your doctor.

Botox may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

When do Botox side effects go away?

It depends. In general, side effects last a few days or weeks, at most. But, how long Botox side effects last varies from person to person. And side effects can also vary depending on the condition you’re using Botox to treat.

If you have side effects that last longer than a few days or weeks, bother you, or become severe, talk with your doctor or pharmacist.

Can Botox cause any brain side effects?

No. People taking Botox in clinical trials didn’t report any side effects that affected the brain.

If you think you’re experiencing side effects that are affecting your brain while taking Botox, call your doctor. They can help determine the cause, and the best treatment for you.

Will I have side effects if I stop using Botox?

Stopping Botox treatment doesn’t cause unique side effects. But as the amount of the drug in your body decreases, symptoms of the condition you were using Botox to treat may develop.

Botox’s effects usually wear off by about 12 weeks after your last dose. Sometimes this can result in your condition coming back or worsening. For example, chronic (long-term) migraine symptoms may get worse than they were prior to Botox treatment after you stop the drug.

If you have questions about stopping Botox, talk with your doctor. They can discuss how stopping treatment may affect your condition.

Learn more about some of the side effects that Botox may cause.

Headache

Headache is a potential side effect of Botox treatment. In clinical trials, headache was more common among people using Botox to treat:

  • chronic (long-term) migraine, which can cause headaches along with other symptoms
  • cervical dystonia (involuntary tightening of neck muscles)
  • axillary hyperhidrosis (excessive underarm sweating)

What you can do

If you have headaches that bother you or concern you while taking Botox, talk with your doctor. They can recommend ways for you to manage this side effect. Or, they may suggest trying a medication other than Botox for your condition.

Urinary retention

Urinary retention is a possible side effect of Botox injections. With urinary retention, you have trouble completely emptying your bladder. This can cause symptoms such as:

  • trouble urinating
  • a burning sensation while urinating
  • frequently feeling like you have to urinate

Urinary retention was more common in people taking Botox to treat:

People taking Botox for the above conditions who have diabetes or multiple sclerosis may be at higher risk for urinary retention.

Your doctor will monitor your urine volume (how much you urinate) within 2 weeks of starting Botox treatment, to check for urinary retention. They may continue to monitor your urine volume for up to 12 weeks.

Botox should only be used to treat bladder problems in people who are able to have a catheter inserted, if needed. A catheter may be used temporarily to help empty your bladder until you no longer experience urinary retention.

What you can do

If you have symptoms of urinary retention, call your doctor. You might need a temporary catheter to treat this side effect.

Before taking Botox for bladder problems, be sure to tell your doctor if you already have urinary retention. Botox may not be right for you if you have this condition, but your doctor can recommend other treatments.

Upper respiratory tract infection

Upper respiratory tract infection is a common side effect of Botox. The common cold is an example of this type of infection. In people taking Botox, these infections are usually mild.

Symptoms of an upper respiratory tract infection may include:

  • cough
  • pressure behind your face
  • runny nose
  • scratchy or sore throat
  • sneezing

This side effect was more common among people taking Botox to treat:

What you can do

If you have symptoms of an upper respiratory tract infection, call your doctor. They can recommend ways to treat this side effect. It isn’t likely that you’ll need to stop taking Botox due to this side effect.

Injection site reaction

Injection site reaction is a common side effect of Botox. This side effect can develop regardless of the condition you’re taking Botox to treat. In clinical trials, it was reported by people taking Botox for:

But, keep in mind injection site reactions may occur when Botox is used to treat other conditions besides those listed above.

Usually, an injection site reaction from Botox is mild and lasts no more than several days.

Symptoms may develop a few hours or days after a Botox injection, and can include:

  • pain
  • tenderness
  • redness or discoloration
  • bruising
  • bleeding

What you can do

If you have an injection site reaction that is severe or bothers you, talk with your doctor about treatments other than Botox that may be better for you.

Spread of toxin effects

Botox has a boxed warning for the drug’s toxin effects spreading away from the injection site. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.

If Botox spreads away from the injection site to other parts of the body, this is called botulism. Botulism can occur hours, days, or even weeks after a Botox injection. Symptoms may include:

In rare cases, botulism can cause trouble breathing or swallowing that’s life threatening. People who already have breathing or swallowing problems may be at higher risk for these severe symptoms.

What you can do

Call your doctor right away if you have problems with breathing or swallowing after a Botox injection. If you think your symptoms may be life threatening, immediately call 911 or your local emergency number.

Allergic reaction

As with most drugs, Botox can cause an allergic reaction in some people. But it’s not clear how often this side effect occurred in clinical trials.

Symptoms can be mild or serious and can include:

  • rash
  • itching
  • flushing
  • swelling under your skin, typically in your lips, eyelids, feet, or hands
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Botox. But if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Botox has some precautions that it’s important to be aware of, including a boxed warning.

Boxed warning: Spread of toxin effects

Botox has a boxed warning about the risk of the drug’s toxin effects spreading away from the injection site, to other parts of the body. This is called botulism.

A boxed warning is the most serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.

For details, see the “Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before you take Botox. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Neuromuscular disorders. People with neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), may be at higher risk for certain side effects of Botox. These may include muscle weakness and trouble breathing. If your doctor decides that Botox is safe for you, they’ll monitor you closely for these side effects.

Active urinary tract infection. If you have an active infection of your urinary tract, you shouldn’t have Botox injections until your infection goes away. Talk with your doctor about treating your infection before you start taking Botox.

Active infection at a Botox injection site. If you currently have an infection of a Botox injection site, you shouldn’t have Botox injections until your infection goes away. Talk with your doctor about treating your infection before you start Botox treatment.

Trouble emptying your bladder. You shouldn’t use Botox to treat urinary incontinence if you can’t fully empty your bladder on your own. However, if you use a catheter to empty your bladder, you may be able to use Botox for urinary incontinence. Talk with your doctor about any trouble emptying your bladder before taking Botox for this purpose.

Upcoming surgical procedures. Be sure to notify your doctor about any upcoming surgical procedures you have before getting Botox injections. Certain anesthesia medications used during surgery could interact with Botox and possibly make Botox less effective. Your doctor can help plan your Botox injections around any upcoming procedures you have.

Allergic reaction. You shouldn’t get Botox injections if you’ve ever had an allergic reaction to Botox or any of its ingredients. Talk with your doctor about which other treatments are better choices for you.

Alcohol with Botox

There aren’t any known interactions between getting Botox injections and drinking alcohol.

Keep in mind that drinking alcohol could cause your risk of certain side effects of Botox, including:

If you drink alcohol, talk with your doctor about how much is safe for you to drink during Botox treatment.

Pregnancy and breastfeeding while taking Botox

It isn’t known if it’s safe to get Botox injections during pregnancy. The drug hasn’t been studied in pregnant people. In animal trials, Botox didn’t cause harm when given to pregnant females. But animal studies don’t always predict what will happen in people.

Talk with your doctor about whether Botox is right for you if you’re pregnant or planning to become pregnant. If you become pregnant after receiving a Botox injection, call your doctor right away.

You should also talk with your doctor about whether Botox is right for you if you’re breastfeeding or planning to breastfeed. It isn’t known whether Botox passes into breast milk. Your doctor can recommend safe ways to feed your child.

Botox can cause side effects in some people. Most mild side effects of Botox go away with time and don’t require medical attention. Serious side effects are also possible.

If you’d like to learn more about Botox, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

  • More information about Botox. For details about other aspects of Botox, refer to this article.
  • Cost. If you’d like to learn about Botox and cost, see this article.
  • Botox for cervical dystonia. For information about Botox treatment for cervical dystonia, refer to this article.
  • Botox for migraine. To learn about Botox treatment for migraine, you can see this article.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.