Side effects in the Mounjaro and Zepbound labels
Mounjaro and Zepbound are FDA-approved medicines made with tirzepatide. Mounjaro is for type 2 diabetes in adults and in children aged 10 and older. It is also approved to lower the risk of heart attack, stroke, and heart-related death in some adults with type 2 diabetes. Zepbound is for weight loss in adults with obesity, or with overweight and a health problem linked to weight. It is also approved for sleep apnea in adults with obesity. Each FDA label lists the side effects seen in its placebo-controlled trials.
In both labels, stomach and bowel problems were the most common. The tables below give the numbers, next to placebo.
In those trials, 4.8% to 6.7% of adults on Zepbound stopped because of side effects. On placebo, 3.4% stopped. Most who stopped did so in the first few months because of stomach and bowel problems.
Each number is the share of people in a group who reported the problem during the trials. Placebo means a shot with no medicine in it. The middle column shows the lowest and highest share across the dose groups. Doses are left out on purpose. Each table lists problems that were more common than on placebo. The Mounjaro table is its label's full list of problems in at least 5% of people on Mounjaro. The Zepbound label lists problems in at least 2% of adults on Zepbound. The table shows the 12 it names as most common, and the other 4 are in the next section.
Trials in the FDA labels
Mounjaro trials in adults with type 2 diabetes 40 weeks
Adults with type 2 diabetes in 2 trials. One tested Mounjaro alone. The other added it to long-acting insulin, with or without metformin. 718 adults took Mounjaro in three dose groups and 235 took placebo. Low blood sugar is left out of this table and covered below.
| Reported problem | Mounjaro groups | Placebo |
|---|---|---|
| Nausea | 12% to 18% | 4% |
| Diarrhea | 12% to 17% | 9% |
| Less appetite | 5% to 11% | 1% |
| Vomiting | 5% to 9% | 2% |
| Constipation | 6% to 7% | 1% |
| Indigestion (dyspepsia) | 5% to 8% | 3% |
| Belly pain | 5% to 6% | 4% |
Source for Mounjaro trials in adults with type 2 diabetes: Mounjaro prescribing information on DailyMed , label revised .
Zepbound trials in adults with obesity or overweight Up to 72 weeks
Adults with obesity or overweight in 2 trials. One trial included only people with type 2 diabetes; the other left them out. 2,519 got Zepbound in three dose groups and 958 got placebo.
| Reported problem | Zepbound groups | Placebo |
|---|---|---|
| Nausea | 25% to 29% | 8% |
| Diarrhea | 19% to 23% | 8% |
| Constipation | 11% to 17% | 5% |
| Vomiting | 8% to 13% | 2% |
| Belly pain | 9% to 10% | 5% |
| Indigestion (dyspepsia) | 9% to 10% | 4% |
| Shot-site reactions, like redness, itching, or bruising | 6% to 8% | 2% |
| Tiredness or weakness (fatigue) | 5% to 7% | 3% |
| Allergic reactions, mostly rash or itching | 5% | 3% |
| Burping | 4% to 5% | 1% |
| Hair loss | 4% to 5% | 1% |
| Acid reflux (GERD) | 4% to 5% | 2% |
Source for Zepbound trials in adults with obesity or overweight: Zepbound prescribing information on DailyMed , label revised .
4 less common problems in the Zepbound trials
More from the Zepbound label
Zepbound trials in adults, less common problems Up to 72 weeks
The same trials and the same groups as the Zepbound table above.
| Reported problem | Zepbound groups | Placebo |
|---|---|---|
| Dizziness | 4% to 5% | 2% |
| Gas | 3% to 4% | 2% |
| Bloated belly | 3% to 4% | 2% |
| Low blood pressure | 1% to 2% | 0% |
Source for Zepbound trials in adults, less common problems: Zepbound prescribing information on DailyMed , label revised .
How this table was chosen
These are the rest of the Zepbound label's list of problems in at least 2% of adults on Zepbound and more common than on placebo. The label does not name them among its most common side effects.
Stomach and bowel problems
In the Zepbound weight trials, 56% of adults on Zepbound and 30% on placebo had a stomach or bowel problem. 1.9% to 4.3% stopped Zepbound because of these problems, compared with 0.5% on placebo.
In the Mounjaro diabetes trials, 37.1% to 43.6% of adults on Mounjaro had a stomach or bowel problem, compared with 20.4% on placebo. 3.0% to 6.6% stopped Mounjaro because of them, compared with 0.4% on placebo.
Both labels say most nausea, vomiting, and diarrhea happened while the dose was being raised and became less common over time.
Some of these problems were severe. In the Zepbound weight trials, severe stomach and bowel problems were reported by 1.7% to 3.1% on Zepbound and 1% on placebo. In the Mounjaro diabetes trials, they were reported by 0.4% to 1.3% on Mounjaro and 0.9% on placebo. Neither label recommends the medicine for people with severe gastroparesis, a condition where the stomach empties very slowly.
Low blood sugar
When Mounjaro was taken alone, no one in the Mounjaro groups had a blood sugar below 54 mg/dL. On placebo, 1% did.
When Mounjaro was added to long-acting insulin, 14% to 19% of the Mounjaro groups had a blood sugar below 54 mg/dL, compared with 13% on placebo. 0% to 2% had low blood sugar that needed another person's help. No one on placebo did.
Low blood sugar was also more common when Mounjaro was taken with a diabetes medicine called a sulfonylurea.
In the Zepbound trial of adults with type 2 diabetes, 4.2% on Zepbound and 1.3% on placebo had a blood sugar below 54 mg/dL. Among people on Zepbound in that trial, it happened to 10.3% of those who also took a sulfonylurea and 2.1% of those who did not. In the trial of adults without diabetes, 0.3% on Zepbound and no one on placebo had a blood sugar below 54 mg/dL. That trial did not check for low blood sugar on a schedule, so this may undercount it. The Zepbound label says it can cause low blood sugar, including in adults without type 2 diabetes.
Allergic and shot-site reactions
In the Mounjaro diabetes trials, allergic reactions were reported by 3.2% on Mounjaro and 1.7% on placebo. Some were severe, such as hives and eczema. Shot-site reactions were reported by 3.2% on Mounjaro and 0.4% on placebo.
Some people make antibodies to tirzepatide. In the Zepbound weight trials, shot-site reactions were reported by 11.3% of people on Zepbound who made these antibodies and 1% of those who did not.
Hair loss
The Zepbound label links hair loss to weight loss. In the weight trials, 7.1% of women and 0.5% of men on Zepbound reported hair loss. On placebo, 1.3% of women and no men did. No one stopped Zepbound because of hair loss.
Gallbladder and pancreas
In the Zepbound weight trials, gallstones were reported by 1.1% on Zepbound and 1% on placebo. A swollen gallbladder (cholecystitis) was reported by 0.7% and 0.2%. In the Mounjaro diabetes trials, sudden gallbladder disease was reported by 0.6% on Mounjaro and no one on placebo.
In the Zepbound weight trials, sudden swelling of the pancreas (acute pancreatitis) was confirmed in 0.2% on Zepbound and 0.2% on placebo. In the diabetes trials, it was confirmed in 13 people on Mounjaro and 3 people on other diabetes medicines or placebo. The label also gives the rate over time: 0.23 compared with 0.11 people per 100 years of use.
In the Zepbound sleep apnea trials, the rate was 0.84 people per 100 years of use on Zepbound and 0 on placebo.
Low blood pressure and kidney injury
In the Zepbound weight trials, low blood pressure was reported by 1.6% on Zepbound and 0.1% on placebo. It was more common in people who also took blood pressure medicine. Sudden kidney injury was reported by 0.5% on Zepbound and 0.2% on placebo. Both labels warn that losing fluid from vomiting or diarrhea can hurt the kidneys.
Heart rate
On average, resting heart rate rose 2 to 4 beats per minute on Mounjaro, compared with 1 beat per minute on placebo. On Zepbound it rose 1 to 3 beats per minute, compared with no rise on placebo.
In the Mounjaro diabetes trials, a fast heart rate with a rise of at least 15 beats per minute was reported by 4.6% to 10% on Mounjaro and 4.3% on placebo. The label says it is not clear how much these rises matter.
Eye problems in people with diabetes
Both labels warn that diabetic eye disease (retinopathy) has gotten worse for a while when blood sugar improved quickly. People who already have this eye disease should be checked for changes, the labels say.
A large heart study
The Mounjaro label also describes a heart study of 6,647 adults with type 2 diabetes and heart disease who took Mounjaro. Side effects were mostly like those in the table. Some were reported more often: less appetite by 17%, constipation by 13%, vomiting by 12%, belly pain by 10%, and tiredness by 10%. The label gives no placebo numbers for this study.
Children with type 2 diabetes
Mounjaro was tested in 97 children aged 10 and older with type 2 diabetes. Side effects were like those in adults, but vomiting, belly pain, and low blood sugar were more common. The 30-week placebo part of that trial tested two doses. Vomiting was reported by 12% to 16% on Mounjaro and 3% on placebo. Belly pain was reported by 15% to 22% on Mounjaro and 9% on placebo.
Low blood sugar below 54 mg/dL was reported by 27% to 30% of children on Mounjaro with long-acting insulin, compared with 10% on placebo. With metformin alone, it was 9% compared with 4%. These groups were small: 10 to 24 children each.
What these numbers do not show
- Both labels have a boxed warning, FDA's strongest kind. Tirzepatide caused thyroid C-cell tumors in rats. It is not known whether it causes them in people, including medullary thyroid cancer (MTC). People with a personal or family history of MTC, or with a condition called MEN 2, must not use it. The labels list signs of a thyroid tumor to watch for: a lump in the neck, trouble swallowing, shortness of breath, or hoarseness that does not go away.
- People who have had a serious allergic reaction to tirzepatide or another ingredient in the product must not use it.
- Both labels list problems reported after approval, such as pancreatitis that can be deadly, blocked bowels, severe constipation, kidney failure, and severe allergic reactions. How often these happen is not known.
- These medicines slow how fast the stomach empties. There are rare reports of people with GLP-1 medicines breathing stomach contents into the lungs during surgery or deep sedation. The labels say to tell the care team before any planned surgery or procedure.
- The labels say these medicines may make birth control pills work less well, mostly in the first weeks and after a dose increase. They advise switching to a non-pill method or adding a barrier method, such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase.
- The Mounjaro label says animal studies suggest there may be risks to an unborn baby. The Zepbound label says weight loss offers no benefit during pregnancy and may harm the baby.
- The Zepbound label does not recommend using it with other tirzepatide products or with any GLP-1 medicine.
- The labels say side-effect rates from one medicine's trials cannot be directly compared with rates from another medicine's trials.
- Trials can miss rare harms and harms that take years to appear.
- These numbers describe Mounjaro and Zepbound. They do not describe compounded tirzepatide or products sold online as research tirzepatide.
Report a side effect
You can report a suspected side effect to the FDA at 1-800-FDA-1088 or through FDA MedWatch . If a reaction feels serious, get medical care first.
Labels checked .
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More about Tirzepatide
Mounjaro and Zepbound have different FDA-approved uses. The full review covers what tirzepatide is, what each product is approved for, and what studies in people show.