If you have type 2 diabetes, your doctor might suggest Mounjaro as a treatment option. It’s a prescription drug used along with exercise and a balanced diet to improve blood sugar levels in adults with type 2 diabetes.

The active ingredient in Mounjaro is tirzepatide. (An active ingredient is what makes a drug work.)

Mounjaro comes as a liquid solution that you inject under your skin. If you and your doctor decide this drug is safe and effective for you, you’ll likely use it long term.

For more information about Mounjaro, including details about its uses, see this in-depth article.

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

Some people may experience mild to serious side effects during their Mounjaro treatment. Examples of Mounjaro’s commonly reported side effects include:

  • nausea and vomiting
  • diarrhea
  • decreased appetite
  • constipation
  • belly pain

Many common side effects of Mounjaro are mild and don’t require medical attention.

Examples of mild side effects that have been reported with Mounjaro include:

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

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

Mounjaro may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

It’s possible to have serious side effects while taking Mounjaro, but they’re not common.

Serious side effects that have been reported with Mounjaro include:

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

* Mounjaro 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 the “Side effects explained” section below.

Get answers to some frequently asked questions about Mounjaro’s side effects.

Does Mounjaro cause dehydration?

Dehydration was not reported as a direct side effect in Mounjaro studies. It’s possible to become dehydrated while using this medication, but it’s rare.

Dehydration can occur because nausea, vomiting, and diarrhea are common side effects of this drug. In most cases, these side effects are mild, but in rare cases, they can be severe. And severe vomiting and diarrhea can lead to dehydration, which may result in kidney problems.

Tell your doctor right away if you have vomiting or diarrhea that does not stop. They can recommend ways to manage these side effects. If needed, they can also provide treatment for dehydration.

Does Mounjaro cause back pain?

No. Mounjaro shouldn’t cause back pain. This side effect wasn’t reported in the drug’s studies.

But certain side effects of Mounjaro may have back pain as a symptom. For example, pancreatitis (inflammation of the pancreas) is a potential side effect of Mounjaro. Symptoms of pancreatitis can include:

If you develop symptoms of pancreatitis while using Mounjaro, let your doctor know right away. They’ll do tests to determine the cause of your symptoms. If they confirm that you have pancreatitis, you’ll likely need to go to the hospital for treatment and stop using Mounjaro.

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

Risk of thyroid cancer

Mounjaro has a boxed warning for the risk of thyroid cancer. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Using Mounjaro may increase your risk of developing thyroid cancer. Mounjaro caused thyroid cancer in animals given this drug in studies. But it’s not clear whether Mounjaro could cause thyroid cancer, such as medullary thyroid cancer (MTC), in humans.

Due to this risk, doctors will not prescribe Mounjaro if you or a family member has had MTC or a condition called multiple endocrine neoplasia syndrome type 2 (MEN 2). This is a rare condition that causes thyroid tumors.

What might help

During your Mounjaro treatment, your doctor may occasionally order blood tests or ultrasounds to check for signs of thyroid cancer. Let them know if you have symptoms of thyroid cancer during your treatment. These can include:

Your doctor will likely have you temporarily stop Mounjaro if you have any of these symptoms. If they confirm that you have thyroid cancer, they’ll likely have you permanently stop taking this drug. In this case, they’ll recommend a different treatment for your diabetes.

Injection site reaction

It’s possible to have an injection site reaction with Mounjaro. This side effect was reported in the drug’s studies. Symptoms at the injection site include:

  • pain
  • swelling
  • redness or skin discoloration

What might help

Injection site reactions with Mounjaro are usually mild and go away on their own.

If you have an injection site reaction, applying an ice pack to the area after your injection may help relieve pain and swelling. Changing the site where you inject the drug each time can also help you avoid injection site reactions. You can inject Mounjaro into your stomach, the top of your thigh, or the back of your upper arm.

Let your doctor know if you have bothersome or painful injection site reactions with Mounjaro. They can discuss injection techniques with you to help prevent these side effects.

They may also recommend over-the-counter (OTC) pain relievers, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol). But always talk with your doctor or pharmacist before taking any OTC drugs to be sure they’re safe for you.

Allergic reaction

Like most drugs, Mounjaro can cause an allergic reaction in some people. Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually 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 a treatment to manage your symptoms. Examples include:

  • an antihistamine you swallow, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Mounjaro, they’ll decide whether 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’ve had a serious allergic reaction to Mounjaro, they’ll likely have you switch to a different treatment.

Keeping track of side effects

During your Mounjaro treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

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

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

Mounjaro has several precautions, including a boxed warning.

Boxed warning: Risk of thyroid cancer

Mounjaro has a boxed warning for the risk of thyroid cancer. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Using Mounjaro may increase your risk of developing thyroid cancer. Due to this risk, your doctor will likely not prescribe this drug if you or a family member has or has had a certain kind of thyroid cancer.

To learn more, see the “Side effects explained” section above.

Other warnings

Mounjaro may not be right for you if you have certain medical conditions. (This is known as a drug-condition interaction.) Other factors may also affect whether this drug is a good treatment option for you.

Talk with your doctor about your health history before starting Mounjaro. Factors to consider include those described below.

Kidney problems. Mounjaro can cause severe nausea, vomiting, and diarrhea, which may lead to dehydration. In some cases, dehydration can cause kidney problems. If you already have kidney problems, Mounjaro may worsen them. Let your doctor know if you have kidney problems before starting this drug. They’ll likely monitor your kidney function closely during your Mounjaro treatment.

Allergic reaction. If you’ve had an allergic reaction to Mounjaro or any of its ingredients, your doctor will likely not prescribe it for you. Ask them about other medications that might be better options.

Pancreatitis. It’s possible to have pancreatitis (inflammation of the pancreas) while you’re using Mounjaro. Your risk may be higher if you’ve already had this condition before. Let your doctor know if you have symptoms of pancreatitis, such as back pain or severe belly pain, while using Mounjaro. They’ll try to determine the cause of your symptoms. If they suspect you have pancreatitis, they’ll likely have you stop treatment with this drug.

Severe digestion problems. Mounjaro has not been studied in people with severe digestion problems, including severe gastroparesis. But Mounjaro slows down movement in your digestive tract. So if you already have this problem, Mounjaro could make it worse. Let your doctor know if you have digestive problems before using Mounjaro. They may recommend a different treatment option for you.

Diabetic retinopathy. Before you start Mounjaro treatment, let your doctor know if you have an eye condition called diabetic retinopathy. Mounjaro can temporarily worsen this condition, so your doctor will likely monitor your vision more closely during your treatment.

Alcohol and Mounjaro

There are no known interactions between alcohol and Mounjaro. But keep in mind that alcohol can cause some of the same side effects as Mounjaro, such as:

  • nausea
  • vomiting
  • diarrhea

Consuming alcohol during your Mounjaro treatment may increase your risk of these side effects or worsen them if they occur.

Alcohol can also increase the risk of hypoglycemia (low blood sugar) in people with diabetes. And alcohol can mask the symptoms of hypoglycemia, a potential side effect of Mounjaro. So drinking alcohol during Mounjaro treatment may cause your blood sugar to become too low. And this condition can be serious, even life threatening, if it’s not treated right away.

If you drink alcohol, talk with your doctor about how much, if any, is safe to consume with this drug.

Pregnancy and breastfeeding while taking Mounjaro

It’s not known whether Mounjaro is safe to use during pregnancy. Studies have not been done on pregnant people using Mounjaro. Let your doctor know if you’re pregnant or planning to become pregnant before starting this drug. They may recommend a different treatment option for you.

It’s not known whether Mounjaro passes into breast milk or what effect it would have on a breastfed child. Before you start Mounjaro treatment, talk with your doctor if you’re breastfeeding or planning to do so. They’ll discuss with you safe ways to feed your child.

Many of Mounjaro’s common side effects are mild and go away on their own after a few days or weeks. But some people may have serious side effects from this medication. It’s important to talk with your doctor before starting Mounjaro treatment. They can answer questions you have about what to expect from this drug.

Here are a few examples of questions you may want to ask your doctor:

  • Is my risk of hypoglycemia (low blood sugar) higher when I first start treatment?
  • How do the side effects of Mounjaro compare with those of Ozempic (semaglutide)?
  • Do I have an increased risk of side effects if I have kidney problems?

To learn more about Mounjaro, see these articles:

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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.