If you’ve recently been prescribed Mounjaro (tirzepatide) to treat your type 2 diabetes, you may be excited to see positive results — both with your blood sugar levels and your weight. But you may also be feeling nervous about how you’ll feel while taking it. After all, GLP-1 medications like Mounjaro have a bit of a reputation for coming with some uncomfortable side effects. But are they that bad? Let’s get a better understanding of what you may expect to feel while on a Mounjaro prescription and what you can do to feel better.
What is Mounjaro?
Mounjaro (tirzepatide) is a GLP-1 FDA-approved to treat type 2 diabetes. While it’s similar to other GLP-1s like Ozempic (semaglutide) and Trulicity (dulaglutide), Mounjaro mimics a second hormone along with the glucagon-like peptide-1 (GLP-1): GIP, which stands for glucose-dependent insulinotropic polypeptide.
“GLP-1 and GIP are hormones that are naturally produced in the body in response to food ingestion,” says Dr. Jacqueline Lonier, M.D., assistant professor of medicine and an endocrinologist specializing in diabetes at Naomi Berrie Diabetes Center at Columbia University. “They help the body make a little more insulin after eating meals to help process glucose and they help people feel full. They’re called satiety hormones. So when we give them in pharmacologic doses, like in Mounjaro, those effects are enhanced.” But even though the medication is mimicking hormones that are already present in the body, getting a bigger dose of them at once may lead to side effects.
Common side effects of Mounjaro
“The main side effects with all of these medications are gastrointestinal in origin,” says Dr. Supriya Rao, M.D., a board-certified physician in internal medicine, gastroenterology, obesity medicine, and lifestyle medicine based in Boston. Here are the most common ones:
- Nausea
- Vomiting
- Constipation
- Loss of appetite
- Diarrhea
A 2023 systematic review and meta-analysis found that of the above, nausea is the most common, happening in just over 20% of people taking Mounjaro. Keep in mind that most of these side effects happen with the first dose or early in Mounjaro treatment and will resolve quickly.
Mild side effects of Mounjaro
While GI-related side effects are the most common with Mounjaro, you may experience some other mild side effects, including:
- Injection site reactions
- Abdominal pain
- Burping
- Dizziness
- Lightheadedness
- Gas
- Fatigue
- Indigestion
- Acid reflux
Rao recommends speaking to your healthcare provider if you’re feeling fatigued, dizzy, or lightheaded so they can check to make sure blood pressure and blood sugars are at the appropriate levels.
Serious side effects of Mounjaro
Even though they’re rare — usually occurring in less than 1% of people — some potential side effects of Mounjaro can be severe and require medical treatment.
- Hypersensitivity, including severe allergic reactions
- Pancreatitis (inflammation of the pancreas)
- Severe digestive problems, which could lead to acute kidney injury
- Acute gallbladder disease
- Increased risk of (relatively rare) medullary thyroid cancer
Explanation of Mounjaro side effects
Not everyone experiences side effects while taking Mounjaro and most of the side effects are relatively mild and won’t last for long. Even so, they can be unpleasant. Following your doctor’s guidance on Mounjaro dosage can help as it lets your body get used to the medication. Lonier recommends starting on the smallest dose of Mounjaro and increasing very gradually in tiny increments. “Going up on the doses slowly, as recommended by the manufacturers, or even more slowly, is also effective,” she says.
Here’s a deeper dive into some of the side effects.
Thyroid cancer risk
Mounjaro carries a black-box warning — a label on medication that alerts people about possible serious or life-threatening side effects — explaining the possible risk of a certain type of thyroid tumor, called medullary thyroid cancer. But there are reasons not to panic. The clinical trials this warning is based on were done on rats that had been given very large doses of a GLP-1 drug, not in humans. “This was a concern in rats and a very specific kind of thyroid tumor called C-cell tumors,” says Lonier. “Most of the majority of thyroid cancers in people are called papillary thyroid cancers. It's a different cell type than the C-cell kind of tumor.”
Tips for managing or identifying thyroid cancer
It’s important that providers are aware of patients’ personal or family history of medullary thyroid cancer. To err on the cautious side, Mounjaro is not recommended in patients with a history or family history of medullary thyroid cancer. Classic symptoms of thyroid cancer include a lump or swelling on the front or side of the neck, trouble swallowing, throat or neck pain, hoarseness in the voice, difficulty breathing, and a lingering cough not caused by a cold or other illness. Let your healthcare provider know right away if you experience any of these symptoms.
Stomach problems
Stomach issues are common while taking Mounjaro, and they can be pretty unpleasant. “I tell people to expect it so they're not surprised and they're not worried that something bad is happening,” Lonier says. The GI issues from taking Mounjaro are due to the very nature of how it works. Slowing down the digestive process keeps food in the stomach longer, which can help people eat less because they feel full for longer, but can also make them feel nauseous.
Tips for managing stomach problems
You want to avoid accidentally overeating, since having too much food sitting in your stomach can make GI problems worse. “The drug makes you feel full much more quickly, so if you limit the size of your meals and your portion sizes, that will help,” Lonier says. This may take some practice. GLP-1 medications cause the stomach to empty more slowly, so you’ll feel full faster than you’re used to.
Avoiding fatty foods can also help. High-fat foods are harder to digest, so when they linger in the stomach for longer, GI upset can occur as a result. Adding more fiber to your diet in the form of whole grains, fruits and vegetables can also help with GI issues like constipation, says Dr. Steven Shamah, M.D., chief of endoscopy and a specialist in obesity management and endoscopic bariatric therapies at Lenox Hill Hospital in New York City.
Pancreatitis
Pancreatitis, or inflammation of the pancreas, is rare, but it has been reported in people taking Mounjaro. While treatable, it requires quick medical intervention. “Pancreatitis has a very classic pain,” Shamah says. “It’s pain right above the belly button, right in the middle [or upper left side], that goes directly to the back.”
Tips for managing pancreatitis
People who are at a higher risk of developing pancreatitis should not take Mounjaro, Shamah says. If you experience the above type of pain, seek medical attention right away. Do not try to “push through” the pain. “You should be going to the emergency room or to your provider to have blood tests and be evaluated and treated,” Shamah says.
Allergic reactions
Some allergic reactions to tirzepatide have been reported. Skin reactions can include hives, redness, rash, or other skin irritation. Symptoms of an allergic reaction to the medication itself include swelling of the tongue, lips or throat, as well as shortness of breath and trouble swallowing. These are serious and require medical attention right away.
Tips for managing allergic reactions
Let your provider know if you have any reaction to Mounjaro. If the reaction is mild on the skin, they may be able to recommend a topical treatment. If the allergic reaction is to the medication itself, the patient should stop taking Mounjaro, seek medical care and consult with their provider about other options.
Anaphylaxis is a life-threatening allergic reaction that requires emergency medical attention. Symptoms develop very quickly, often in minutes or even seconds. These include difficulty breathing or swallowing; swelling of the face, tongue, or eyes; vomiting; abdominal pain; and losing consciousness.
The bottom line
Mounjaro is an effective medication for managing type 2 diabetes, but it can cause some side effects. Most of these are GI-related — nausea, constipation, vomiting — and won’t take long to go away on their own. Eating small meals, avoiding fatty foods, and consuming plenty of fiber can help. Although rare, some people may experience more severe side effects, including severe allergic reactions, pancreatitis, gallbladder disease, and acute kidney injury. Talk to your doctor if you’re concerned about any symptoms or side effects when taking Mounjaro.
FAQs
Mounjaro can increase insulin production to help regulate blood glucose and lower A1C levels. It also reduces your appetite by slowing down gastric emptying and targeting certain receptors in your brain, which is why people often lose weight when taking it.
Mounjaro should not be taken with an insulin secretagogue, as it can increase the risk of hypoglycemia (low blood sugar).
It depends on the person, but most side effects resolve relatively quickly. They are usually worse when you go up in a dose or right after you give yourself the injection. Some patients might not experience any side effects, while others may have ones that are so unpleasant that they can’t continue the medication.
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This content is for informational purposes only and does not constitute medical advice, diagnosis or treatment. It should not be regarded as a substitute for guidance from your healthcare provider.