Tirzepatide Side Effects by Dose: What the Trials Recorded

In the trials behind Zepbound, stomach and bowel side effects hit about the same share of people at every maintenance dose: 56% on 5 mg, 10 mg and 15 mg, against 30% on placebo. What changed with dose was the kind and severity. Vomiting and diarrhea rose from 5 mg to 15 mg, constipation fell, and more people stopped the drug because of side effects at the higher doses.

GI events by dose

The label pools two 72-week placebo-controlled trials, SURMOUNT-1 in adults without diabetes and SURMOUNT-2 in adults with type 2 diabetes. It lists every adverse reaction that occurred in at least 2% of tirzepatide patients and more often than on placebo¹.

Three patterns stand out. Nausea barely moves above 5 mg: it was 25% on the lowest maintenance dose and 28% on the highest. Vomiting climbs steadily, from 8% to 13%. Constipation runs the other way, 17% on 5 mg and 11% on 15 mg, while diarrhea rises from 19% to 23%.

Hair loss deserves a note, because it worries people. The label ties it to weight reduction rather than to the drug directly, and it was reported far more in women, 7.1%, than in men, 0.5%. No tirzepatide patient in the pooled trials stopped treatment because of it¹.

Why tirzepatide causes diarrhea, and why it usually fades

The label does not give a single mechanism for diarrhea. What it does state is that "tirzepatide delays gastric emptying," and that it acts on GIP and GLP-1 receptors, including in brain regions that regulate appetite¹. Slower emptying explains nausea, fullness and burping well. The bowel effects are less well explained. The same drug gives some people diarrhea and others constipation, and across doses the two moved in opposite directions.

The timing is clearer than the mechanism. The label says "the majority of nausea, vomiting, and/or diarrhea events occurred during dose escalation and decreased over time." The SURMOUNT-1 paper reported that most GI events were mild to moderate and happened "primarily during dose escalation"¹². That is why the label starts everyone at 2.5 mg for four weeks and raises the dose by 2.5 mg no faster than every four weeks. It says this schedule is meant "to reduce the risk of gastrointestinal adverse reactions." The 2.5 mg dose is a starting step and is not approved for maintenance¹.

Discontinuation for adverse events

Two sets of numbers circulate here. They describe different groups, so they don't match.

The pooled label figures rise with dose. SURMOUNT-1 alone peaks at 10 mg. That is the sort of difference that happens when a few dozen people separate the arms, and it is not a finding that 10 mg is worse than 15 mg. The steadier signal is in the GI rows: both the share who stopped for GI reasons and the share with severe GI reactions climb from 5 mg to 15 mg¹².

For scale, the same SURMOUNT-1 paper reported mean weight changes at 72 weeks of -15.0%, -19.5% and -20.9% on 5, 10 and 15 mg, against -3.1% on placebo². In SURMOUNT-2, in people with type 2 diabetes, few adverse events led to stopping (under 5%), and serious adverse events were reported by 7% of participants overall³.

What the label warns about

The warnings are not dose-by-dose, but they apply at every dose.

• Thyroid C-cell tumors. The boxed warning says tirzepatide causes these in rats and "it is unknown whether ZEPBOUND causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans." It is contraindicated with a personal or family history of MTC or MEN 2¹.
• Severe GI reactions. Zepbound "is not recommended in patients with severe gastroparesis"¹.
• Acute kidney injury from fluid loss, reported in 0.5% on tirzepatide against 0.2% on placebo in the pooled trials¹.
• Gallbladder disease. Cholecystitis was reported in 0.7% against 0.2%¹.
• Acute pancreatitis. It was confirmed in 0.2% in both arms of the weight-loss pool, and post-marketing reports include fatal cases¹.
• Hypoglycemia, mainly with insulin or sulfonylureas. It was reported in 4.2% against 1.3% in the diabetes trial¹.
• Diabetic retinopathy in people with type 2 diabetes, and pulmonary aspiration under anesthesia or deep sedation¹.

The label also changed in 2026. The severe-GI warning was revised in February 2026, and the retinopathy warning in August 2026. The earlier warning on suicidal behavior and ideation is listed as removed as of February 2026¹.

Compounded tirzepatide is not the trial drug

Every rate on this page comes from Lilly's product, made to its approved specification, injected by trial participants on a fixed escalation schedule. A compounded vial is a different product: a different formulation, from a pharmacy whose output FDA has not reviewed for this use, often at doses and schedules no trial tested. The side-effect table describes the drug in the trial, not the vial.

Compounding has also narrowed. FDA said in April 2026 that "tirzepatide and semaglutide do not currently appear on the 503B bulks list or on FDA's drug shortage list." A 503A pharmacy may still compound tirzepatide only within FDA's limits on copies of commercially available drugs⁴. The full picture is in compounded is not the trial drug and compounding status by peptide.

What the trials did not measure

The trial tables answer a narrow question: fixed doses of 5, 10 or 15 mg, reached by the label's escalation, for up to 72 weeks. Several things people ask about fall outside it.

• The in-between doses. 7.5 mg and 12.5 mg were escalation steps, not randomized maintenance arms, so no side-effect rate is published for staying on them.
• Faster or slower escalation than the label's four-week steps, split doses, and "microdosing." None was a trial arm.
• Use beyond the trial periods. The longest exposure the label describes is up to 88 weeks in the withdrawal trial¹.
• Anyone on compounded tirzepatide, as above.

For how tirzepatide compares with semaglutide on both weight loss and tolerability, see semaglutide vs tirzepatide. The trial record for the molecule is on the tirzepatide page. Companies that prescribe it are compared on the tirzepatide board, which shows what each one actually dispenses.