Botox (onabotulinumtoxinA) is a prescription medication with a variety of uses. If you have one of the conditions that Botox is used to treat, your doctor may recommend this drug for you.

This article describes Botox’s use for medical purposes. To learn more about the drug’s use for cosmetic reasons, check out this article.

Botox is used to:

Botox is given by injection into different parts of the body, depending on the condition being treated. Your doctor or other healthcare professional will give you the injections. In most cases, you’ll get Botox injections every 12 weeks on a long-term basis.

For more information about Botox, including a full list of conditions it’s used to treat, see this in-depth article on the drug.

Like other drugs, Botox can cause mild or serious side effects. Keep reading to learn more.

Side effects of Botox can vary depending on which condition the drug is being used to treat. Below are some of the more common side effects reported by people who used Botox in studies.

More common side effects in adults using Botox for migraine include:

  • neck pain
  • headache*

More common side effects in adults using Botox for axillary hyperhidrosis include:

  • pain or bleeding at the injection site
  • sweating in other parts of the body

More common side effects in people using Botox for limb spasticity include:

More common side effects in adults using Botox for cervical dystonia include:

  • trouble swallowing*
  • upper respiratory infections, such as the common cold

More common side effects in adults and children using Botox for blepharospasm or strabismus include:

More common side effects in people using Botox for bladder problems include:

*To learn more about this side effect, see “Side effects explained” below.

Examples of mild side effects that have been reported with Botox used for any condition include:

  • injection site reactions*
  • muscle weakness close to where Botox is injected
  • flu-like symptoms such as fever, nausea, and achy muscles

Other mild side effects of Botox can vary depending on which condition the drug is being used to treat. Here are some examples of mild side effects reported by people who received Botox for different conditions in studies.

Mild side effects in adults using Botox for migraine include:

Mild side effects in people using Botox for axillary hyperhidrosis include:

  • sweating in other parts of the body
  • sore throat
  • headache*
  • neck or back pain
  • itching

Mild side effects in people using Botox for limb spasticity include:

Mild side effects in people using Botox for cervical dystonia include:

  • upper respiratory infections, such as the common cold
  • neck or back pain
  • headache*
  • dizziness
  • dry mouth

Mild side effects in people taking Botox for blepharospasm include:

Mild side effects in people using Botox for strabismus include:

  • drooping eyelid

Mild side effects in people using Botox for bladder problems include:

*To learn more about this side effect, see “Side effects explained” below.

In most cases, these side effects should be temporary. And some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. And don’t stop using Botox unless your doctor recommends it.

Botox may cause mild side effects other than the ones listed above. See the Botox medication guide for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Botox, visit MedWatch.

Serious side effects that have been reported with Botox include:

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.

* Botox has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects explained” section below.
† To learn more about this side effect, see “Side effects explained” below.

The most common side effects reported in adults using Botox for chronic migraine include:

  • neck pain
  • headache*
  • drooping eyelid
  • muscle aches and pains
  • muscle stiffness or weakness
  • pain at the injection site

Other less common side effects reported in adults using Botox for migraine include:

If you’re concerned or have questions about possible side effects of taking Botox to treat migraine, talk with your doctor.

*To learn more about this side effect, see “Side effects explained” below.

Here are answers to some frequently asked questions about Botox’s side effects.

Does Botox cause any long-term side effects?

Yes. Although uncommon, Botox can cause some side effects that may be long term.

Possible long-term side effects of Botox include:

  • urinary retention (not being able empty your bladder on your own) in people taking Botox for bladder problems
  • corneal ulceration (open sore on the front of the eye) in people taking Botox for blepharospasm

If you’re concerned about possible long-term side effects with Botox, talk with your doctor.

When do side effects from Botox typically go away?

Most side effects from Botox usually go away after a few days or weeks as the effects of the injection wear off. But this may vary depending on the condition being treated, the specific side effect, and how your body reacts to the drug.

If you have side effects that are troublesome or that last longer than a few days or weeks, talk with your doctor.

Could Botox cause any side effects that affect my brain?

No, Botox isn’t known to cause side effects that affect or damage the brain.

The toxin effects of Botox can sometimes spread from the area where the injections are given,* causing a condition called botulism. This condition involves widespread problems with the way nerves communicate with muscles. But this doesn’t affect the brain.

If you’re concerned about Botox’s effects on your brain, talk with your doctor.

* Botox has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects explained” section below.

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

Headache

Some people may have a headache after receiving Botox injections. In studies, headache was common in people using Botox for migraine, axillary hyperhidrosis, or cervical dystonia. This side effect wasn’t reported in people who used Botox for other conditions.

What might help

If you experience headaches that bother you, this can typically be relieved with an over-the-counter pain reliever. Examples include acetaminophen (Tylenol) or ibuprofen (Advil, Ibu-Tab, Motrin). You can ask your pharmacist to recommend a medication that’s safe for you.

Avoiding alcohol may also help prevent headaches during your Botox treatment.

If you get a headache, you should avoid massaging or rubbing your head, neck, or shoulders if you’ve had Botox injections in these areas. Rubbing or massaging a Botox injection site can raise your risk for the toxin spreading to other areas. See the section directly below to learn more about this.

Spread of toxin effects

Botox has a boxed warning for the spread of toxin effects. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

Botox can sometimes spread from the area where the injections are given. This can cause a serious condition called botulism.

Botulism can occur hours, days, or even weeks after receiving a Botox injection. Symptoms of botulism can include:

The spread of toxin effects is rare, but it may be more likely to occur in people receiving Botox for limb spasticity, especially children.

The spread of toxin effects hasn’t been reported in people using recommended doses of Botox for migraine, excessive sweating, blepharospasm or strabismus. To learn more, see the drug’s prescribing information.

What might help

After you’ve had Botox injections, avoid rubbing or massaging the area where you had the injections for a couple of days. This will help avoid spreading the toxin into other areas.

If you have symptoms of botulism after receiving Botox, call your doctor right away, even if it’s been several days or weeks since your last injection. You may need treatment in a hospital.

It’s especially important to get medical help right away if you have trouble breathing, swallowing, or speaking after having Botox injections. If your symptoms feel life threatening, call 911 or your local emergency number.

You shouldn’t drive if you have symptoms such as blurred or double vision, drooping eyelid, dizziness, or muscle weakness.

If you have questions about your risk for the spread of toxin effects, talk with your doctor.

Injection site reactions

Some people may experience reactions at the site where Botox injections are given. In studies, this side effect was reported in people who received Botox to treat migraine, axillary hyperhidrosis, limb spasticity, and cervical dystonia.

Symptoms of injection site reactions can include:

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

Injection site reactions typically develop in the week after receiving injections. They’re usually mild and improve in a few days. But in some cases, they can last longer.

What might help

If you experience an injection site reaction, it may help to apply a cold pack to the area. This can help reduce any pain, swelling, or bruising. You should avoid rubbing or massaging the area where you had the injections for a few days after receiving Botox. This will help avoid spreading the toxin into other areas. (See “Spread of toxin effects” directly above to learn more.)

If you have injection site reactions that are severe, troublesome, or last for a long time, talk with your doctor. They may be able to suggest ways to help manage this side effect.

Urinary retention

Botox can cause urinary retention when it’s used to treat bladder problems such as urinary incontinence (loss of bladder control) or overactive bladder.

With urinary retention, you can’t fully empty your bladder on your own. This can cause symptoms such as:

  • frequently feeling like you need to urinate
  • trouble urinating
  • burning sensation when urinating

In studies, urinary retention was commonly reported in adults receiving Botox injections to treat bladder problems. People with diabetes or multiple sclerosis may have a higher risk for urinary retention with Botox.

Urinary retention wasn’t reported in children receiving Botox injections for bladder problems. But these studies only involved children who were already using a catheter to empty their bladder.

What might help

Urinary retention is treated by inserting a catheter into your bladder to allow it to empty. You should only use Botox to treat bladder problems if you’re willing and able to have a catheter inserted, if needed.

Your doctor will check you for urinary retention within 2 weeks of when you receive Botox injections. They’ll typically do this by taking an ultrasound scan of your bladder after you’ve urinated. This gives an estimate of the amount of urine that’s still in your bladder after urination. Your doctor may continue to monitor you with these bladder scans for up to 12 weeks.

If you have symptoms of urinary retention, call your doctor right away. You may need a temporary catheter to help empty your bladder until you no longer have urinary retention.

Allergic reaction

Like most drugs, Botox can cause an allergic reaction in some people.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine), or a topical product, such as hydrocortisone cream, to manage your symptoms.

If your doctor confirms you had a mild allergic reaction to Botox, they’ll decide if you should continue using it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you had a serious allergic reaction to Botox, they may have you switch to a different treatment.

Keeping track of side effects

During your Botox treatment, consider keeping notes on any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful to do when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of drug you were taking when you had the side effect
  • how soon after starting that dose you had the side effect
  • what your symptoms were from the side effect
  • how it affected your daily activities
  • what other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help your doctor learn more about how this drug affects you. Your doctor can use this information to adjust your treatment plan if needed.

Botox is used in certain children to:

  • treat blepharospasm (uncontrollable blinking or twitching of the eyelid)
  • treat strabismus
  • treat upper or lower limb spasticity
  • treatneurogenic detrusor overactivity (overactive bladder caused by a nerve problem)

In studies, side effects of Botox in children with blepharospasm or strabismus were similar to those seen in adults who used Botox for these conditions. The most common side effect is drooping eyelid.

Side effects of Botox in children with limb spasticity or an overactive bladder may be slightly different than side effects seen in adults with these conditions.

For example, in studies, upper respiratory infection (such as the common cold) were more common in children than in adults who took Botox for limb spasticity. Upper respiratory infections are the most common side effect in children who use Botox for this condition.

The most common side effect in children and adults using Botox for bladder problems was urinary tract infection (UTI). Urinary retention (not being able empty your bladder on your own) was also common in adults receiving Botox for bladder problems.

Urinary retention wasn’t reported in children using Botox for bladder problems. But in these studies, children receiving Botox for this condition were already regularly using a catheter to empty their bladder.

To find out more about possible side effects of Botox in children, talk with your child’s doctor.

This drug comes with several warnings.

Boxed warning: Spread of toxin effects

Botox has a boxed warning for the spread of toxin effects. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Botox can sometimes spread from the area where the injections are given. This can cause a serious condition called botulism. To learn more, see the “Side effects explained” section above.

Other warnings

Botox may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you take Botox. The list below includes factors to consider.

Allergic reaction. If you’ve ever had an allergic reaction to Botox or any of its ingredients, you shouldn’t be given Botox. Ask your doctor what other medications are better options for you.

Infection at the injection site. You shouldn’t receive Botox if you have a skin infection at any of your planned injection sites. Your treatment will be delayed until the infection gets better. Your doctor can determine if you need medication to treat the infection.

Urinary tract infection (UTI). If you’re taking Botox to treat a bladder problem, you shouldn’t receive injections if you have a UTI. Your treatment will be delayed until the infection gets better. Your doctor can also determine if you need medication to treat the infection. If you get UTIs often, talk with your doctor about whether Botox is right for you.

Urinary retention. Botox can cause urinary retention (not being able empty your bladder on your own) when used to treat bladder problems. If you already have urinary retention, you shouldn’t receive Botox to treat bladder problems. (But if you already use a catheter to empty your bladder, this warning doesn’t apply.) If you have trouble emptying your bladder, talk with your doctor about whether Botox is right for you.

Neuromuscular disorders. If you have a neuromuscular disorder, such as amyloid lateral sclerosis (ALS), Lambert-Eaton myasthenic syndrome, or myasthenia gravis, you may have a higher risk for certain side effects with Botox. Examples of these side effects include muscle weakness, drooping eyelid, double vision, and trouble speaking, swallowing, or breathing. If you have a neuromuscular disorder, talk with your doctor about whether Botox is right for you. If you do use this drug, your doctor may want to monitor you more closely during your treatment.

Breathing or swallowing problems. Botox can sometimes spread from the area where it’s injected and cause trouble breathing or swallowing. These problems can be life threatening, especially if you already haveproblems with breathing or swallowing. Talk with your doctor about whether this treatment is right for you.

Planned surgery. Certain medications that may be used during surgery could raise your risk for side effects from Botox. If you have any surgeries planned, talk with your doctor about whether it’s safe to receive Botox around the time of your surgery.

Alcohol use and Botox

It should be safe to drink alcohol during your Botox treatment. But doing so may raise your risk for certain side effects, such as headache, dizziness, nausea, or fatigue.

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

Pregnancy and breastfeeding while taking Botox

It’s not known if it’s safe to have Botox injections during pregnancy. It’s also not known if Botox gets into breast milk, or whether it can affect a child that’s breastfed.

If you’re pregnant or breastfeeding, or are planning to become pregnant or to breastfeed, talk with your doctor about whether Botox is right for you.

Botox can be an effective treatment for the conditions it’s used to treat. But as with all drugs, it’s possible to have side effects with Botox.

If you’re thinking about using Botox to treat your condition, talk with your doctor about possible side effects you may have. This can help you decide if this treatment is right for you. Examples of questions you might want to ask include:

  • Do I have a higher risk than others for certain serious side effects, such as trouble swallowing or breathing?
  • If I get side effects with Botox, should I stop getting the injections?
  • What could happen if I get pregnant during my Botox treatment?

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Disclaimer: Healthline 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.