Tirzepatide Side Effects
Tirzepatide is the active ingredient in two once weekly injections: Mounjaro, approved for type 2 diabetes, and Zepbound, approved for weight management and for obstructive sleep apnea in adults with obesity. Because the ingredient is the same, the side effect profile is shared. This page explains that shared profile from the two FDA approved labels, and where the brand pages go deeper. It is education only, not medical advice.
One ingredient, two brands
Mounjaro and Zepbound are the same drug, tirzepatide, sold under two names for different uses. Tirzepatide works on two gut hormone receptors, GIP and GLP-1, which is part of why its effect on appetite and blood sugar is strong. The tirzepatide dosage chart shows the shared escalation pattern both brands follow. Each brand also has its own detailed guide on this site: Mounjaro side effects and Zepbound side effects.
The shared side effect profile
Across both labels, the reactions reported most often are gastrointestinal, which fits how tirzepatide works: it slows stomach emptying and reduces appetite. The shared core list is:
- Nausea. The most frequently reported reaction on both labels.
- Diarrhea. Reported most often while the dose is being increased.
- Vomiting. Often connected to dose increases or eating past fullness.
- Constipation. A natural counterpart to slower digestion.
- Stomach pain and indigestion. Abdominal pain and dyspepsia both appear on the labels.
- Reduced appetite. Part of how the medicine works, and itself a listed reaction.
- Injection site reactions and fatigue. Both appear among the reported reactions.
Hair loss also appears among the reactions reported in the tirzepatide trials and is listed on the Zepbound label. Shedding on these medicines is usually tied to rapid weight loss itself, as our GLP-1 hair loss guide explains.
Why the two labels read a little differently
The Mounjaro and Zepbound labels are close but not identical. The brands were studied in different groups of people: the Mounjaro trials were in people with type 2 diabetes, while the Zepbound trials were in people with overweight or obesity, and later in people with obstructive sleep apnea. Different study populations surface slightly different reactions, and each label carries some warnings that matter most for its own use, such as the low blood sugar discussion on the diabetes label. The underlying profile of the ingredient is the same.
Warnings that appear on the tirzepatide labels
Boxed warning: thyroid C-cell tumors. Both labels carry the strongest FDA warning, about a possible risk of thyroid C-cell tumors. In animal studies, tirzepatide caused these tumors in rats. It is not known whether it causes them in people. The labels say the medicines should not be used by people with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2.
Pancreatitis. Inflammation of the pancreas has been reported. Severe stomach pain, sometimes spreading to the back, is the warning sign the labels describe.
Gallbladder problems. Gallstones and gallbladder inflammation have been reported, and rapid weight loss itself raises gallstone risk.
Severe stomach problems. Because tirzepatide slows stomach emptying, the labels note it has not been studied in people with severe gastroparesis and is generally not recommended for them.
Allergic reactions. Serious allergic reactions, including anaphylaxis and swelling of the face, lips or tongue, have been reported.
When to get medical care promptly
Whichever brand is used, some symptoms should never be waited out. Seek medical care promptly for severe or persistent stomach pain, signs of an allergic reaction such as swelling of the face, lips or tongue or trouble breathing, yellowing of the skin or eyes, or a lump or swelling in the neck, a hoarse voice, or trouble swallowing. Ongoing vomiting or diarrhea that stops you drinking enough fluid also deserves a prompt call, because dehydration can strain the kidneys.
Frequently asked questions
Are Mounjaro and Zepbound the same drug?
They contain the same active ingredient, tirzepatide. Mounjaro is approved for type 2 diabetes, and Zepbound for weight management and for obstructive sleep apnea in adults with obesity. Each brand has its own label, but the ingredient, and the way it works in the body, are the same.
What are the most common tirzepatide side effects?
Across both labels, the most commonly reported reactions are gastrointestinal: nausea, diarrhea, vomiting, constipation, stomach pain, indigestion and reduced appetite. Injection site reactions and fatigue also appear, and hair loss is listed on the Zepbound label. These effects are reported most often while the dose is being increased.
Does tirzepatide cause hair loss?
Hair loss appears among the reactions reported in the tirzepatide trials and is listed on the Zepbound label. Shedding during treatment is usually linked to the rapid weight loss itself, a well known trigger for temporary shedding, rather than a direct effect of the medicine on hair. Our GLP-1 hair loss guide explains the mechanism in more detail.
Are tirzepatide side effects the same for both brands?
Largely, yes. Both labels name the same core group of stomach and digestion reactions. The wording and emphasis differ a little because the brands were studied in different groups of people, for different conditions, and each label carries some warnings that matter most for its own use.
What is the boxed warning for tirzepatide?
Both the Mounjaro and Zepbound labels carry a boxed warning about thyroid C-cell tumors. In studies, tirzepatide caused these tumors in rats. It is not known whether it causes them in people. The labels say the medicines should not be used by people with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2.