Mounjaro (tirzepatide) is a once-weekly injectable medicine that helps people with type 2 diabetes keep their blood sugar under control. It also causes weight loss. If you’ve seen the dramatic effects it can have on people, you might be wondering, “What does Mounjaro do to your body?”
It changes the way your body digests food, and it can cause quite a few side effects in the process. Not everyone who uses Mounjaro has side effects. You may not have some or even any of them, but you should still know what to look out for just in case.
What Is Mounjaro?
Mounjaro is the brand name of tirzepatide, an injectable type 2 diabetes medicine. Tirzepatide also has FDA approval, under the brand name Zepbound, to help people lose weight when they have obesity and a weight-related health problem like high blood pressure or high cholesterol.
These drugs are similar to, but not exactly the same as, other diabetes and weight loss injectables you might have heard of, called Ozempic and Wegovy. Like these drugs, Mounjaro slows the movement of food through your digestive system.
In the body, Mounjaro acts like two hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). These hormones play important roles in blood sugar control, appetite, and digestion. By comparison, Ozempic and Wegovy only mimic GLP-1.
GLP-1 helps lower blood sugar and makes you feel full faster and for longer after you eat. GIP increases your body’s release of insulin, which is needed to turn the sugar in your blood into energy and keep it from building up in the bloodstream.
Gastrointestinal Side Effects of Mounjaro
Since it significantly slows down your gut, Mounjaro can come with some uncomfortable GI side effects. For most people, the symptoms are mild to moderate and go away after your body gets used to the medicine. People usually have these symptoms when they first start Mounjaro and each time they raise their dose.
Mounjaro and nausea
In clinical trials, up to 22% of people on Mounjaro – just over 1 in 5 – had nausea. Up to 1 in 10 people reported vomiting, too. Larger doses are more likely to cause these side effects.
Try these tips to relieve nausea from Mounjaro:
- Only eat when you’re hungry, which may be much less often than before you started the medicine.
- Stop eating as soon as you feel full, which might happen a lot sooner than you expect.
- Eat more frequent, smaller meals throughout the day, rather than three larger ones.
- Eat slowly.
- Avoid greasy, high-fat foods, which may digest more slowly and make the side effect worse.
- Have crackers, apples, and mint- or ginger-based drinks about a half-hour after taking the medication.
- For severe nausea or vomiting, don’t drink with meals. Limit beverages to 30 to 60 minutes before or after meals.
- Avoid strong smells, like those of cleaning products.
Mounjaro and diarrhea
In clinical trials, about 12% to 17% of people had diarrhea when taking Mounjaro.
You might ease or prevent diarrhea if you avoid:
- Full-fat dairy
- Coffee, alcohol, soft drinks, and sports drinks
- High-fiber foods while you have symptoms – you can bring them back as symptoms improve.
Make sure you:
- Choose leaner-protein and blander foods, such as chicken (baked or grilled, not fried).
- Choose blander foods like broth, rice, carrots, very ripe peeled fruits, and cooked fruits.
- Drink plenty of water.
Mounjaro and constipation
That slow digestion that Mounjaro causes can lead to a backup in your colon. About 1 in 13 people on Mounjaro complain of constipation.
The standard rules of thumb for relieving constipation from any cause apply here, too.
Make sure you’re doing these things:
- Drinking plenty of fluids, mostly water. Aim for 91 to 125 ounces every day.
- Exercising every day
- Adding fiber to your diet with at least two servings a day of fruits, vegetables, or whole grains
A dosage adjustment might also help. Ask your doctor.
Mounjaro and heartburn
In Mounjaro clinical trials, just over 2% of people – or 1 in 50 – had heartburn, acid reflux, or GERD. The acid might come from vomiting or from backed-up or slowed digestion.
Here are some ways to prevent or lessen heartburn:
- Avoid triggers like spicy, fried, or greasy foods, caffeine, and alcohol.
- Eat slowly.
- Eat small meals.
- Stay upright for at least 2 hours after meals.
- Sleep with your head and upper body slightly raised.
- Try sleeping on your left side.
- If you smoke, quit.
More Common Side Effects of Mounjaro
Besides GI discomfort, you might have a few other mild side effects from Mounjaro.
Injection site reactions
Just over 3% of people – or 1 in 30 – in clinical trials for Mounjaro had injection site reactions. That’s when the skin around the area where you inject the drug gets red, painful, or irritated.
The redness and pain usually go away on their own. But if you need something for the discomfort, you can try an ice pack, cold compress, or an over-the-counter anti-inflammatory, like ibuprofen.
Mounjaro and dizziness
Some people feel dizzy or lightheaded when they take Mounjaro. This could be a sign of low blood sugar (hypoglycemia). If you take Mounjaro along with other blood sugar-lowering drugs, such as insulin or sulfonylureas, you are at risk of low blood sugar. If you have low blood sugar while taking Mounjaro, ask your doctor what you should do. You might need to change the way you use your other diabetes medicine.
Dizziness or fainting can also be a sign of a serious allergic reaction to Mounjaro. If you have an allergic reaction, stop taking the medicine and get medical help right away. Other signs of an allergic reaction include:
- Swelling in your face, lips, tongue, or throat
- Trouble breathing or swallowing
- Itching or a rash
- A fast heartbeat
Can Mounjaro affect your mood?
A small number of people taking Mounjaro have reported mood changes, including depression, anxiety, and suicidal thoughts.
A 2024 study in the International Journal of Clinical Pharmacy looked at 31,444 reports of these side effects in people taking GLP-1 drugs Mounjaro/Zepbound, Victoza/Saxenda (liraglutide), or Ozempic/Wegovy (semaglutide). Just 2% of the reports came from Mounjaro users. All other complaints were dividedly pretty evenly between the other two drugs, with slightly more coming from Victoza users. None of the psychiatric-related deaths were among Mounjaro/Zepbound users.
All of that said, safety warnings about the drug do indicate that it can cause agitation, crankiness, and other abnormal behaviors. There have been some reports of suicidal thoughts from people taking this medication. But further investigation from the FDA has found no evidence of a connection between the diabetes medication and suicidal thoughts or tendencies.
Still, it’s a good idea to note that if, after starting this medicine, you have sudden strong feelings, such as feeling nervous, angry, restless, violent, or scared, you should tell your doctor right away.
Also keep in mind that anxiety, crankiness, and other mood changes can be signs of low blood sugar. Remember: If you take Mounjaro along with other blood sugar-lowering drugs, you’re at increased risk of that.
Serious Side Effects of Mounjaro
In rare cases, some people taking Mounjaro have had more serious side effects. Here’s what you should know.
Mounjaro and pancreatitis
Pancreatitis, inflammation of the pancreas, can start and end suddenly or become an ongoing problem.
Relatively very few cases of pancreatitis have been reported among Mounjaro users – about 23 per 1,000 new users per year. Some research suggests that the risk linked to the medicine is negligible.
But you should know the signs of this potentially deadly condition. If you have sudden belly pain that doesn’t get better, especially pain that radiates to your back, tell your doctor. If the pain is so bad you can’t sit still, go to an emergency room or urgent care.
Mounjaro and thyroid cancer
Mounjaro comes with an FDA “black box” warning that the drug has caused both cancerous and non-cancerous thyroid tumors in mice and rats. The higher the dose and the longer they were on the medication, the higher the risk for tumors.
It’s not yet known whether the medication might have the same effect on people, but it isn’t recommended for people who have a personal or family history of thyroid cancer.
If you’re taking Mounjaro, and you have any of the following symptoms, tell your doctor:
- A lump or swelling in your neck
- Hoarseness
- Trouble swallowing
- Shortness of breath
Mounjaro and stomach paralysis
Other medicines that work like Mounjaro by slowing down digestion have, in rare cases, caused stomach paralysis, also known as gastroparesis. While it’s not listed as a risk of this specific medicine, some lawsuits underway are representing Mounjaro users who developed it.
With this condition, the stomach begins to empty so slowly that some food never makes it into the intestines. This food may harden and form solid masses in your stomach that could cause pain or block your intestines or bowels.
Paralysis may also cause whole undigested pieces of food to move into your intestines, which can be painful and difficult to pass through a bowel movement.
The signs of stomach paralysis include:
- Indigestion
- Bloating
- Feeling full very quickly or for a long time after eating
- Upper belly pain
- Nausea and throwing up
- Whole pieces of undigested food in your vomit or poop
- Loss of appetite
- Acid reflux or heartburn
- Blood sugar fluctuations
- Constipation
If you don’t act, stomach paralysis can lead to malnutrition, dehydration, and a life-threatening blockage in your bowels. Tell your doctor if you have signs of this condition.
Mounjaro and kidney disease
Mounjaro’s effect on the kidneys isn’t entirely clear. In the clinical trial that earned Mounjaro its FDA approval, there were some reports of kidney damage from the drug. But more recently, research has come out saying that Mounjaro prevents kidney disease.
Discuss your risk with your doctor.
Mounjaro and hypoglycemia
In the clinical trial, about 1% to 2% of people who were taking Mounjaro in addition to insulin got dangerously low blood sugar. Mounjaro treats diabetes by increasing insulin and lowering blood sugar. If you take other blood sugar-lowering medications at the same time, such as insulin or sulfonylureas, there’s a chance your blood sugar could get too low (hypoglycemia).
Ask your doctor if you should change the dose or timing of your other blood sugar-lowering medicine before you start Mounjaro.
Mounjaro and vision changes
Mounjaro can bring about rapid changes to your blood sugar. This can change the shape of the lenses of your eyes and cause blurry vision for a few months while your body adjusts.
If you have diabetic retinopathy, your doctor should carefully watch over your eyes and vision while you take Mounjaro. The medicine could make your retinopathy worse for a while.
Mounjaro and bowel obstruction
Studies of GLP-1 drugs that slow digestion, the way Mounjaro does, have shown that an intestinal blockage, also called a bowel obstruction or ileus, is a rare but serious risk of taking these medications. But the large studies that have measured this risk didn’t include Mounjaro users. They looked at the rates of bowel obstruction in users of other GLP-1 drugs.
Bowel obstructions can happen when something physically blocks the intestines, like a mass of hardened food caused by stomach paralysis. It can also happen because the contractions of the intestines become so weak that they can no longer move food through.
If not treated in time, a blockage can be deadly. Know the signs:
- A distended or expanded belly
- Gas, especially that you’re unable to pass
- Belly pain or cramping
- Bad breath
- Constipation
- Diarrhea
- Vomiting
If you suspect you have an obstruction, tell your doctor right away.
Mounjaro and gallbladder problems
In clinical trials, about 1 in 200 people on Mounjaro got acute gallbladder disease. That refers to gallstones or inflammation of the gallbladder (usually caused by gallstones).
Beware of the signs of gallstones:
- Steady, severe, and rapidly increasing belly pain that lasts from 30 minutes to several hours
- Pain in the back between the shoulder blades
- Pain in the right shoulder
Get medical care right away if you have the following signs:
- Sweating
- Chills
- A low fever
- Yellowing of the skin or whites of the eyes
- Clay-colored poop
Mounjaro and Allergic Reactions
Some people who’ve taken Mounjaro have had serious allergic reactions. If you’ve had severe allergic reactions in the past, tell your doctor before you start it.
Allergic reactions happen shortly after you take the medicine. If you have any of the following right after your dose, get medical help right away:
- A rash, itching, or hives
- Swelling in your lips, tongue, or throat
- Shortness of breath, trouble breathing, or wheezing (a whistling sound during breathing)
- Dizziness or fainting
- Stomach pain, bloating, vomiting, or diarrhea
- Uterine cramps
- Feeling like something awful is about to happen
Mounjaro Long-Term Side Effects
Because Mounjaro and similar diabetes injectables are so new, experts don’t know much about whether they may have long-term side effects. Your risk of long-term side effects may depend in part on your individual health. Discuss your risk with your doctor.
Managing Mounjaro Side Effects
The most common side effects of Mounjaro affect your GI tract. Making changes to what you eat and how you eat can go a long way to help manage those side effects.
Diet changes on Mounjaro
When you avoid certain foods and lean into others, you can help prevent nausea, vomiting, heartburn, diarrhea, and constipation.
Try these tips:
- Eat foods that are boiled, baked, or grilled.
- Eat water-rich foods, like melons, bell pepper, cucumber, and celery.
- Drink clear drinks.
- Avoid high-fat and full-fat foods.
- Avoid sweets, dressings, spicy foods, and canned foods.
It will also help to change some of your eating habits.
Try these:
- Eat slowly.
- Take small sips and don’t use a straw.
- Eat small portions.
- Eat more frequent, smaller meals, rather than three larger ones.
- Eat only when you’re hungry and stop as soon as you’re full.
- Don’t lie down for at least 2 hours after a meal.
- Don’t eat close to bedtime.
- Don’t do heavy exercise after meals.
- Do light physical activity after meals to help food get moving.
- Keep a food diary to identify triggers of your GI symptoms.
How long do Mounjaro side effects last?
The slow digestion and decreased appetite that Mounjaro causes will last for as long as you take the drug. Most GI symptoms should go away in about a month, but they might come back for a while when you increase your dose.
Who Shouldn’t Take Mounjaro?
You shouldn’t take Mounjaro if you have:
- Had thyroid cancer
- A strong family history of thyroid cancer
- Multiple endocrine neoplasia syndrome II
- A severe allergic reaction to it
- Allergies to any of the drug’s ingredients
When to Call Your Doctor About Mounjaro Side Effects
If you have ongoing side effects that don’t go away with time and diet changes, talk to your doctor. You might be able to take over-the-counter medicine for your symptoms. Your doctor might also adjust your dose to help you.
Side effects that require more urgent medical attention are:
- Symptoms of a severe allergic reaction
- Signs of thyroid tumors
- Severe belly pain
Mounjaro Side Effects Takeaways
- GI problems are the most common side effects of Mounjaro.
- Most GI problems go away within a few weeks or a month as your body gets used to the medicine.
- Serious side effects are rare but possible. If you have signs of them, tell your doctor or seek help right away.
Mounjaro Side Effects FAQs
Q: What are the cons of taking Mounjaro?
A: Mounjaro can cause very uncomfortable GI side effects. It also comes with risks of other much more serious side effects. You’ll need to discuss your individual risk with your doctor as well as the risks of not taking this medicine.
Q: What does Mounjaro do to your body?
A: It slows your digestion, curbs your appetite, increases your insulin, and lowers your blood sugar. All of these help control your diabetes and cause weight loss.
Q: Does Mounjaro cause constipation or diarrhea?
A: Mounjaro can cause both of these side effects. You can help prevent them with diet and lifestyle changes. They should also work themselves out after your body is used to the medicine.
