Tirzepatide side effects: what is common and what is serious

The stomach effects most people notice first

Tirzepatide has two labels with two side effect tables. Zepbound covers weight and sleep apnea; Mounjaro covers type 2 diabetes ^{[4] [5]}. Because each table comes from a different trial population, the rates do not match. Here are the Zepbound weight-trial rates on 5, 10 and 15 mg, each set against placebo ^[1]:

• Nausea: 25%, 29% and 28% (placebo 8%)
• Diarrhea: 19% to 23% (placebo 8%)
• Constipation: 11% to 17% (placebo 5%)
• Vomiting: 8% to 13% (placebo 2%)
• Indigestion and belly pain: 9% to 10% each (placebo 4% to 5%)
• Skin reactions where you inject: 6% to 8% (placebo 2%)
• Tiredness 5% to 7% (placebo 3%); dizziness 4% to 5% (placebo 2%)

Mounjaro's diabetes trials logged lower stomach rates on the same three doses: nausea 12% to 18% and diarrhea 12% to 17% ^[5]. The brand pages go row by row: Zepbound side effects lists the whole weight-trial table, and Mounjaro side effects covers the diabetes trials.

Why your stomach reacts, and for how long

Part of the answer is mechanical. The label says tirzepatide delays gastric emptying, so meals sit in the stomach longer ^[1]. It also works on GIP and GLP-1 receptors in parts of the brain that steer appetite and food intake ^[1]. SURMOUNT-1 found the gut effects were usually mild or moderate and showed up mostly during dose increases ^[2], which fits the label's slow ramp: 2.5 mg to start, and no step up sooner than 4 weeks ^[4]. The ramp is laid out on tirzepatide dosage.

We found no source that puts a number of days or weeks on nausea or diarrhea. What the Medication Guide does say: keep drinking fluids so you are less likely to get dehydrated, and phone your prescriber promptly when nausea, vomiting or diarrhea will not settle ^[6]. Eating and drinking tips that stay within the label are on tirzepatide diet.

Hair, energy, headaches and mood

Hair loss

Shedding was reported by 5%, 4% and 5% on the three doses, compared with 1% on placebo; by sex, 7.1% of women and 0.5% of men ^[1]. Nothing in the label says how long shedding lasts or whether it grows back. Mention it to your prescriber. What trials show after people come off the drug is on stopping tirzepatide.

Tiredness

Tiredness showed up in 5% to 7% of Zepbound users, vs 3% of people on placebo ^[1]. Nowhere does the label claim the drug boosts energy.

Headaches, dizziness and shakiness

Headache does not appear in the Zepbound list of common reactions; dizziness does, at 4% to 5% against 2% ^[1]. The Medication Guide groups headache, dizziness, sweating, shakiness and anxiety as possible clues to low blood sugar, which is mostly a concern when tirzepatide is combined with insulin or a sulfonylurea ^[6].

Anxiety, depression and mood swings

Depression and anxiety are absent from the Zepbound common-reaction list ^[1], and the Medication Guide brings up mood changes only as a clue to low blood sugar ^[6]. In February 2026 the Zepbound label dropped its suicidal behavior and ideation warning ^[4]. Even so, report new or worsening mood symptoms to your prescriber, and call 911 if you might harm yourself.

Insomnia, joint pain, dry mouth, periods and erections

The Zepbound common-reaction list includes none of these ^[1]. That tells you they were not frequent enough in trials to make the list; it does not prove they never happen. For people who use the pill for birth control, the Mounjaro label adds a caution: tirzepatide can make oral contraceptives work less well, so it suggests a non-oral method or an added barrier method for 4 weeks after the first dose and after every dose increase ^[5]. More on tirzepatide interactions.

The serious list: thyroid, pancreas, gallbladder, eyes

Does tirzepatide cause cancer?

Yes, there is a cancer warning, and it sits in a box at the top of the label. In rats, tirzepatide caused thyroid C-cell tumors, more with higher doses and longer use; nobody knows yet whether it does the same in humans, including a cancer called medullary thyroid carcinoma (MTC) ^[1]. People who have had MTC, or have a relative who did, or who have Multiple Endocrine Neoplasia syndrome type 2, must not take it. Tell your prescriber about a lump in the neck, hoarseness that lingers, trouble swallowing or shortness of breath ^[1]. The label's pancreas warning is about acute pancreatitis (inflammation), not pancreatic cancer ^[1].

Pancreatitis and gallbladder disease

If you get stomach pain that is severe and does not let up, whether or not you are vomiting, stop the drug and call your prescriber straight away; the pain can spread to your back ^[6]. Acute gallbladder disease is also among the label's warnings ^[1]. Watch for pain high in the belly, fever, yellowing of skin or eyes, and pale, clay-colored stools ^[6].

Vision and blindness

This warning applies to type 2 diabetes. When blood sugar improves quickly, diabetic retinopathy has sometimes worsened for a while ^[4]. The Medication Guide asks people with type 2 diabetes to report any change in vision ^[6]. We did not find blindness listed as a side effect in the label sections we checked.

Low blood sugar, dehydration and blood pressure

Without diabetes, low blood sugar (below 54 mg/dL) was rare: 0.3% on tirzepatide, 0% on placebo. With type 2 diabetes the figures were 4.2% and 1.3%, rising to 10.3% for people who also took a sulfonylurea ^[1]. Losing fluid through vomiting or diarrhea can dehydrate you and strain the kidneys ^[6]. Low blood pressure turned up in 1.6% on Zepbound vs 0.1% on placebo ^[1].

Allergic reactions, hives and itching

Allergic-type (hypersensitivity) reactions were logged in 5% vs 3% on placebo ^[1]. Stop using it and get help immediately if your face, lips, tongue or throat swell, if breathing or swallowing gets hard, or if you have a severe rash or itch, faint or feel dizzy, or notice a racing heartbeat ^[6].

Muscle loss and soreness

Some of the weight that comes off is lean mass. A SURMOUNT-1 substudy scanned 160 people: at 72 weeks fat mass was down 33.9% and lean mass 10.9%, so lean tissue made up about one quarter of the loss ^[7]. The label puts it as more fat lost than lean mass ^[1]. Sore muscles, body aches and back pain are not on the Zepbound common-reaction list ^[1]. Ideas for protecting muscle: how to keep muscle on a GLP-1.

Sleep apnea is an approved use, not a side effect

Sleep apnea is something Zepbound treats. FDA approved it for moderate to severe obstructive sleep apnea in adults with obesity, the first drug cleared for that group ^[8]. Across two 52-week trials the apnea-hypopnea index (breathing pauses per hour) dropped by 25.3 and 29.3 events, compared with 5.3 and 5.5 on placebo ^[1].

Tirzepatide vs semaglutide side effects

SURMOUNT-5 put tirzepatide and semaglutide head to head, and stomach events were the top side effects in both arms ^[9]. Its abstract does not declare either drug easier to tolerate. Label tables are a weaker comparison because they come from different trials: Wegovy 2.4 mg nausea was 44% (placebo 16%) ^[10], Zepbound 25% to 29% (placebo 8%) ^[1]. Different people, different studies, so do not line these up directly. More on Wegovy vs Zepbound and GLP-1 side effects.

Compounded tirzepatide: outside these numbers

All the rates above describe the FDA-approved brands. Compounded tirzepatide is a different matter: it is not FDA-approved, and FDA does not check compounded drugs for safety, effectiveness or quality ^[3]. By May 31, 2026 FDA had more than 730 adverse event reports tied to compounded tirzepatide, and it expects the real figure is higher because 503A pharmacies do not have to report ^[3]. FDA has also described patients measuring compounded injectable semaglutide wrongly ^[3]; compounded tirzepatide vials carry the same measuring risk. See compounded tirzepatide and our FDA warning letter tracker.

Is the stomach a good place to inject?

It is one of three labeled spots. The others are the thigh and, when a second person gives the shot, the back of the upper arm; move to a new spot every week ^[5]. Reactions at the injection site affected 6% to 8% on Zepbound and 2% on placebo ^[1]. Label steps are on how to use tirzepatide.