Mounjaro Side Effects: Why Do They Happen? What Can You Do?

Learn about the side effects of Mounjaro and how to manage them. Find out what you can do to avoid common side effects and when to seek medical attention.
Medical Reviewer: Elizabeth Lowden, MD
Published on: September 18, 2023
Updated on: December 20, 2023

Learn more about how FORM pairs patients with a doctor and dietitian to achieve their weight loss goals.

What are Mounjaro side effects?

WHAT YOU'LL LEARN

Disclaimer: The content made available on The FORM Medical Weight Loss Blog represents the views and opinions of the authors and not those of other entities, such as the manufacturers of products mentioned therein. 

Obesity is a complex, chronic disease that affects nearly half of adults in the United States. MounjaroⓇ, which is currently only FDA-approved for the treatment of adults with type 2 diabetes, has become one of the most promising medications for the treatment of obesity. Clinical trials have shown that patients lost around 26% of total body weight when combined with lifestyle intervention. While Mounjaro offers promising benefits for weight loss, it is important to be aware of the potential side effects, which can range from mild to serious in nature. In this article, we will review both common and rare side effects of Mounjaro and how to minimize the risk of developing these side effects.

What is Mounjaro Used For?

Mounjaro, which contains the active ingredient tirzepatide, is a once-weekly injectable medication that is used along with diet and exercise to improve blood sugar in adults with type 2 diabetes. Unlike other type 2 diabetes medication, it is the first single molecule that mimics two naturally occurring hormones in the body: glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Mounjaro activates both the GIP and GLP-1 receptors throughout the body, which improves insulin sensitivity, stimulates insulin release, slows down stomach emptying, and reduces food intake. The dual action of Mounjaro on GIP and GLP-1 receptors produces a synergistic effect, which combined with lifestyle changes can lead to reduced blood sugar as well as weight loss.

Common Side Effects of Mounjaro

While Mounjaro is a safe and effective medication for most people, like with any medication, there are potential side effects that need to be taken into consideration. Common side effects of Mounjaro include, but are not limited to, nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion, and stomach pain. Most gastrointestinal symptoms occur after initiating treatment or adjusting the dose and typically go away after a few days or weeks as the body builds a tolerance to each dose.

Serious Side Effects of Mounjaro

While most of the side effects of Mounjaro are benign and transient in nature, there are some rare but serious side effects that need to be taken into consideration.

Mounjaro has a boxed warning for the risk of medullary thyroid cancer. A boxed warning alerts healthcare providers and patients about the most serious side effects a drug may cause. Similar to GLP-1 medications, Mounjaro caused thyroid tumors, including medullary thyroid cancer, in rodent studies. It is unknown whether Mounjaro will cause thyroid tumors, or this type of thyroid cancer, medullary thyroid carcinoma (MTC), in humans. Due to this risk, Mounjaro should not be used in patients with a personal or family history of MTC or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

Other serious side effects of Mounjaro include:

Pancreatitis: Symptoms of inflammation of the pancreas may include severe mid upper abdominal pain that may radiate to the back, nausea, and vomiting. Stop using Mounjaro and get medical help right away.

Hypoglycemia: Low blood sugar can occur if Mounjaro is used in combination with insulin or sulfonylureas (e.g., glyburide, glimepiride, glipizide), or other medications that can cause low blood sugar. Signs and symptoms of hypoglycemia may include dizziness, sweating, confusion, blurred vision, shakiness, fast heartbeat, irritability, hunger, weakness, and jitteriness. Monitor blood sugars regularly and follow up with your healthcare provider for medication dose adjustment.

Serious allergic reaction: Symptoms of serious allergic reaction may include swelling of the lips, tongue, throat, or face, difficulty breathing or swallowing, severe rash or itching, and fainting or feeling lightheaded. Stop using Mounjaro and seek medical attention right away.

Kidney injury: Severe diarrhea and vomiting can lead to fluid loss, which may cause decline in kidney function. Drink plenty of fluids to prevent dehydration while taking Mounjaro.Changes in vision: Monitor for any vision changes during treatment with Mounjaro. Alert your healthcare provider if you experience changes in vision.

Gallbladder disease: Symptoms of gallbladder problems may include right upper abdominal pain, fever, yellowing of the skin or eyes, and clay-colored stools. Tell your healthcare provider right away if you develop these symptoms.

Side Effects Depending on Mounjaro Dosage

Though generally well tolerated, different dosages of Mounjaro trigger different adverse events rates. The SURMOUNT-1 clinical trial evaluated the safety of tirzepatide in adults with obesity or overweight who did not have diabetes. The most commonly reported side effects were gastrointestinal-related, occurring primarily during dose increases. These side effects generally improve with continued use.

  • For those treated with 5 mg of tirzepatide, 24.6% experienced nausea, 18.7% experienced diarrhea, 16.8% experienced constipation, and 8.3% experienced vomiting.
  • For those treated with 10 mg of tirzepatide, 33.3% experienced nausea, 21.2% experienced diarrhea, 17.1% experienced constipation, and 10.7% experienced vomiting.
  • For those treated with 15 mg of tirzepatide, 31.0% experienced nausea, 23.0% experienced diarrhea, 11.7% experienced constipation, and 12.2% experienced vomiting.
  • Compared to placebo, 9.5% reported nausea, 7.3% reported diarrhea, 5.8% reported constipation, and 1.7% reported vomiting.

These side effects are important to consider when choosing a treatment plan, and Mounjaro is not appropriate for everyone. The decision to start a medication should be discussed with your healthcare provider. It is important to work with a medical weight loss program that understands your health history and goals in order to develop a treatment plan that is safe and effective for you.

How to Minimize the Risk of Mounjaro Side Effects

Mounjaro side effects will vary from person to person and can be affected by many factors, including medical history, medications, and lifestyle.

To reduce the risk of side effects, Mounjaro is started at the lowest dose of 2.5 mg weekly. After 4 weeks, it is increased to 5 mg. Additional dose increases may occur depending on how well it is tolerated. The dose is typically increased by 2.5 mg increments every 4 weeks up to the maximum dosage of 15 mg weekly. If a dose is not well tolerated, it may be advised to stay at the current dose for a longer period of time before increasing further or to decrease the dose. Many of these side effects can be managed with dietary and lifestyle adjustments.


For patients taking insulin or sulfonylureas, speak with your healthcare provider about reducing the dose of these medications to reduce the risk of hypoglycemia. Mounjaro may potentially affect the absorption of oral medications so close monitoring is indicated. For patients taking oral contraceptives, use an additional form of birth control for 4 weeks after initiation and for 4 weeks after each dose escalation as Mounjaro can decrease the effectiveness of oral contraceptives. 

When Should You See a Doctor?

While many of the side effects of Mounjaro can be managed with dietary and lifestyle changes, patients should seek immediate medical attention should they experience any of the serious side effects listed above while taking Mounjaro. A healthcare provider can help patients navigate these potential side effects and determine the proper course of treatment. For common gastrointestinal side effects, your doctor may be able to prescribe anti-nausea medication or recommend over the counter medications to help manage these side effects.

Take Control of Your Health: Mastering Mounjaro Side Effects with Confidence

Like with any medication, it is important to be aware of the potential side effects of Mounjaro, which can range from mild to potentially serious. Side effects are common with dose initiation and dose escalation and typically improve over time. Mounjaro should be taken under medical supervision to ensure its safety and tolerability. 

At FORM, we conduct a thorough intake at your first appointment including your medical history and lab work to ensure that Mounjaro is safe and appropriate for you. FORM patients have access to their dedicated Care Team via messaging in the FORM app to ask any questions or share concerns about side effects. Our comprehensive approach includes personalized lifestyle and medical support to help you manage the potential side effects of Mounjaro. If you are interested in learning whether Mounjaro is a good option to help you achieve your weight loss and health goals, schedule a call or send a message to FORM to learn more. You can also take our quiz to find out if you are eligible. 

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