Taking Mounjaro? What to Know About Side Effects

Whether you’re taking Mounjaro (tirzepatide) for type 2 diabetes management or you’ve been prescribed the version of this drug approved for weight loss (Zepbound), you might encounter side effects. That’s especially true if you’re gradually increasing the dosage, which is a common strategy with Mounjaro and related drugs as a way to optimize the drug’s effects, says Caroline Messer, M.D., an endocrinologist at Northwell Lenox Hill Hospital in New York City.

In some cases, the adverse effects will resolve on their own as your body gets used to the medication, Dr. Messer says; if not, there are often ways to alleviate the issues so they don’t interfere too much with your everyday life. Here’s what to know.

Mounjaro works by mimicking two hormones in the body, according to the National Library of Medicine: glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which are involved in stimulating insulin secretion and decreasing glucose production when you eat. By targeting both of them, Mounjaro decreases appetite and slows the rate of digestion as a way to increase satiety. First approved in 2022 for treating type 2 diabetes, the active ingredient in Mounjaro, tirzepatide, got a new approval at the end of 2023 for weight loss in adults with an initial body mass index (BMI) of 30 or higher (obesity) or BMI of at least 27 (overweight) with one or more weight-related co-existing condition, such as heart disease, high cholesterol, high blood pressure, obstructive sleep apnea, or type 2 diabetes.

According to the drug’s manufacturer, Eli Lilly and Co., and the U.S. Food and Drug Administration (FDA), these are the side effects most commonly reported among people taking Mounjaro. You’ll notice that most of the effects are GI-related. We’ve added tips from physicians about what might help alleviate each issue. Note that you may experience side effects that aren’t on this list.

Nausea

This is the most commonly reported side effect of Mounjaro. In clinical trials of the drug, 18% of patients taking the highest dose of Mounjaro (15 milligrams injected once a week) reported nausea, per the FDA. And about half that number of patients reported vomiting at that dosage.

The maker of Mounjaro noted that in the trials, nausea and vomiting tended to occur while the dose of the drug was being increased. The typical starting dose of Mounjaro is 2.5 mg once weekly for 4 weeks before increasing to 5 mg for at least 4 weeks, then higher as needed; the goal of starting at the 2.5 mg dose is to reduce GI symptoms while the body adjusts to the drug (this dosage does not provide effective weight loss or glycemic control).

What you can do: Along from exercising patience while your body adjusts to each dose, Dr. Messer recommends some specific ways to reduce nausea and subsequent vomiting. These include:

• Adjust what you eat.“While no foods are strictly contraindicated, processed, high-sugar and fatty foods are likely to worsen side effects like nausea and gastrointestinal distress,” she says.

• Limit alcohol. “Alcohol not only worsens nausea, it is likely to exacerbate reflux by relaxing the sphincter that separates the stomach from the esophagus,” Dr. Messer says. Alcohol may also cause a drop in blood sugar, she adds, which is why it’s advisable to limit or avoid drinking alcohol while you’re on the medication (since Mounjaro also lowers blood sugar).

• Eat more fiber. Nausea may also be reduced by tacking another common side effect, which is constipation. With constipation, secondary issues like nausea and bloating are common, says Dr. Messer. Focusing on increasing your fiber intake through foods like fruits, vegetables, and whole grains, can help alleviate both problems, she adds. “The general recommendation is 38 grams of fiber per day for men and 25 grams per day for women,” she says.

• Eat smaller, more frequent meals. “For reducing nausea, some patients find it useful to eat five small meals throughout the day rather than three larger meals,” Dr. Messer says. “In addition, I recommend eating slowly and stopping before the point of satiety.”

• Stay hydrated. “[I advise patients to] make sure to stay hydrated throughout the day because dehydration can cause nausea or make it worse,” Dr. Messer says.

Other Digestive Problems

Mounjaro may play a role in causing challenges at any point along your digestive trajectory—which includes your esophagus, stomach, intestines, rectum, and anus as well as your liver, pancreas, and gallbladder. In clinical trials, common digestive effects reported by people taking Mounjaro included:

• Abdominal pain

• Constipation

• Decreased appetite

• Diarrhea

• Excessive or frequent burping

• Flatulence

• Heartburn or acid reflux

What you can do: “Alleviating [digestive] side effects often requires consultations with registered dietitians, educators, and therapists who have expert knowledge about medication effects, as well as appropriate diet and beverage use,” says Meena Murthy, M.D., chief of the division of endocrinology, nutrition, and metabolism at Saint Peter’s University Hospital in New Brunswick, NJ.

“These professionals can also offer guidance on necessary behavior modifications that can help support you in implementing this medication more successfully,” she adds. For example, they might recommend eating smaller meals more frequently, adding moderate physical activity, and choosing foods that are less likely to cause digestive symptoms.

Injection Site Reactions

Because Mounjaro is taken via injection—usually into the abdomen, upper arm, or thigh—you may experience irritation at the place where you inject the drug or in the surrounding area. Symptoms might include:

• Itching

• Lump or thickened area under the skin

• Numbness

• Rash

• Skin redness or discoloration

• Soreness, tenderness, or pain at the site

• Warmth at the injection site

According to data from the FDA, 3.2% of people on Mounjaro reported injection site reactions during placebo-controlled clinical trials of the drug, compared to 0.4% taking placebo.

What you can do: You can minimize the effects with strategies like rotating the site where you inject the medication each week and avoiding areas that are itchy or red. To reduce swelling and irritation, try applying an ice pack or cool cloth on the site after injection.

In addition to the side effects listed above, there are some less common side effects that you should also watch for, and alert your doctor if they occur. According to the Mayo Clinic, these may include:

• Coldness

• Difficulty swallowing

• Fast heartbeat

• Feeling of pressure in the abdomen

• Hair loss

• Loss of fat volume in the face

• Muscle weakness

• Recurrent fever

• Tingling in the hands or feet

• Tiredness or fatigue

According to Mounjaro’s prescribing information, the drug can cause rare but serious side effects including:

• Allergic reactions: Like most medications, Mounjaro may prompt an allergic reaction that could become severe, including trouble breathing, rash, hives, and swelling of the face or throat.

• Diabetic retinopathy: This condition is caused by damage to the blood vessels in the tissue at the back of the eye. Symptoms include blurred vision, seeing spots, or vision loss.

• Emotional changes: Some people become agitated, angry, restless, violent, or fearful when taking Mounjaro, and some experience depression or have suicidal thoughts.

• Kidney failure: In people who have existing kidney failure or kidney disease, taking Mounjaro may worsen those conditions if diarrhea and vomiting are causing dehydration. Signs include bloody urine, decreased urine output, rapid weight gain, and swelling of the face, ankles, or hands.

• Pancreatitis: Mounjaro may cause swelling of the pancreas, which can cause sudden and severe stomach pain, chills, vomiting, fever, or lightheadedness.

• Severe nausea and vomiting: For some people, nausea is not resolved with strategies like eating smaller meals or changing food selections, and they may experience frequent vomiting. They may require an anti-nausea medication or may need to discontinue Mounjaro if this side effect doesn’t resolve.

• Stomach paralysis: Also known as gastroparesis, this condition is caused by food taking too long to leave the stomach, resulting in hardened masses that could lead to blockages in the intestine.

• Thyroid tumors: Tirzepatide has been shown to cause thyroid C-cell tumors in animal studies, which increases the risk of medullary thyroid carcinoma (a type of thyroid cancer). However, this effect has not been seen in humans.

These effects are considered rare. Still, it’s important to let your doctor know about any family history of problems such as thyroid cancer or kidney disease before you start Mounjaro, says Mir Ali, M.D., a bariatric surgeon at Orange Coast Medical Center in Fountain Valley, CA.

Also, pay attention to how the medication is affecting your mental health in addition to as your physical health. If you are noticing changes in your emotional state, that’s essential information for your doctor to know.

It’s important to keep in mind that side effects of Mounjaro may intensify or be more likely if you’re taking other medications, including insulin or other drugs to lower blood sugar. In that case, your Mounjaro dose may need to be increased more gradually to reduce the risk of hypoglycemia (low blood sugar). Even vitamin and mineral supplements may work differently than they did before you started taking Mounjaro, Dr. Murthy says.

“Mounjaro delays stomach emptying, so that may interfere with absorption of other medications and supplements,” she says. “Because of that, you’ll need careful assessment and monitoring if you’re on any medication in addition to Mounjaro.”

An important note if you are taking oral contraceptives: Dr. Murthy says Mounjaro may decrease the effectiveness of oral contraceptives by delaying gastric emptying. So if you’re taking those to prevent pregnancy, it’s crucial to talk with your physician about adding other prevention methods for four weeks after starting the drug and four weeks after any dose increase, per the FDA. Research indicates this is not true with other GLP-1 medications such as semaglutide (Ozempic, Wegovy), so it seems to be a unique complication for tirzepatide specifically.

According to a 2023 analysis by Prime Therapeutics, which manages pharmacy benefits, more than two-thirds of people who are prescribed a GLP-1 receptor agonist for weight loss are no longer taking it after a year. For many, that discontinuation can come as a result of discomfort from side effects, says Dr. Murthy.

At that point, it’s common for people to regain weight that was lost while on the medication, she adds. In a study in the journal JAMA of overweight or obese individuals who took tirzepatide, researchers found that such regain can be substantial, with participants who took tirzepatide for 36 weeks and then switched to a placebo gaining back an average of 14% of their body weight over the following year. (In contrast, those who remained on tirzepatide lost another 5.5% of their weight during that period.)

Because obesity is considered a chronic condition, much like hypertension or diabetes, these medications are designed to be used long term, says Dr. Ali. If you do have to stop taking them (whether because of side effects or other reasons), creating mindful strategies around eating, talking to a registered dietitian nutritionist, and getting more physical activity can all help reduce the risk of weight regain, he says. However, he adds, it’s possible that rather than stopping GLP-1 drugs altogether, another option might be to try switching to a different one and seeing if it’s easier to tolerate. Additionally, keep in mind that these medications are meant to be used as an adjunct to reduced-calorie diet and increased physical activity (not a replacement for them) for best results.

Mounjaro and related medications like Ozempic, Wegovy, and Zepbound are rapidly changing how diabetes and obesity are managed as well as perceived. But like any drugs, it’s important to know about potential effects as you’re considering your choices.

While many side effects might be uncomfortable, they tend to become resolved within a few weeks of starting the meds or increasing the dose, says Dr. Ali. However, if side effects are not decreasing over time, check in with your doctor so you can implement strategies to prevent those effects from worsening, Dr. Messer adds.

“If symptoms such as constipation or diarrhea last more than a few days, talk to your doctor,” she says. In addition, “you should contact your doctor if you’re having severe right upper quadrant abdominal pain after eating or intractable nausea and vomiting,” she says. Upper quadrant pain could be a sign of gallstones or another gallbladder problem, she adds.

And get emergency treatment—meaning call 911 or go to the emergency room—if you’re experiencing a severe reaction, particularly trouble breathing or another sign of a serious allergic response.