Tirzepatide is one drug sold under two names, and the side-effect numbers you see depend on which label they came from. Zepbound's trials enrolled people with obesity or overweight, mostly without diabetes. Mounjaro's enrolled people with type 2 diabetes. The figures below come from both current US labels, dated August 2026 [1] [2]. For the molecule itself, see our tirzepatide guide.
Tirzepatide is sold as Zepbound and Mounjaro, and their trials enrolled different people
- Zepbound treats weight long term in adults with obesity, or overweight plus a weight-related condition, and treats moderate to severe obstructive sleep apnea in adults with obesity [1]. See our Zepbound guide.
- Mounjaro improves blood sugar in adults and children 10 and older with type 2 diabetes, and since August 2026 lowers the risk of heart attack, stroke and heart-related death in adults with type 2 diabetes at high risk [2]. See our Mounjaro guide.
Both labels start at 2.5 mg once a week and allow up to 15 mg. Your prescriber decides the dose steps in between. The populations differ in ways that move the numbers, so read each label's rates against its own placebo group.
Digestive effects lead both lists, and they're more frequent in the weight trials
| Side effect | Zepbound placebo | Zepbound 5–15 mg | Mounjaro placebo | Mounjaro 5–15 mg |
|---|---|---|---|---|
| Nausea | 8 | 25–29 | 4 | 12–18 |
| Diarrhea | 8 | 19–23 | 9 | 12–17 |
| Vomiting | 2 | 8–13 | 2 | 5–9 |
| Constipation | 5 | 11–17 | 1 | 6–7 |
| Abdominal pain | 5 | 9–10 | 4 | 5–6 |
| Indigestion (dyspepsia) | 4 | 9–10 | 3 | 5–8 |
| Decreased appetite | not in table | not in table | 1 | 5–11 |
| Injection-site reactions (incl. bruising on Zepbound) | 2 | 6–8 | 0.4 | 3.2 (pooled) |
| Fatigue | 3 | 5–7 | not in table | not in table |
| Allergic-type (hypersensitivity) reactions | 3 | 5 | 1.7 | 3.2 (pooled) |
| Burping (eructation) | 1 | 4–5 | 0.4 | 2.5–3.3 |
| Hair loss | 1 | 4–5 | not in table | postmarketing |
| Heartburn and reflux (GERD) | 2 | 4–5 | 0.4 | 1.7–2.5 |
| Gas (flatulence) | 2 | 3–4 | 0 | 1.3–2.9 |
| Bloating (abdominal distension) | 2 | 3–4 | 0.4 | 0.4–2.9 |
| Dizziness | 2 | 4–5 | not in table | not in table |
| Low blood pressure | 0 | 1–2 | not in table | not in table |
Zepbound Table 1 (Studies 1 and 2, up to 72 weeks) and Mounjaro Table 1 and §6.1 (SURPASS-1 and -5), DailyMed version 40 for each, August 2026. Ranges run across the 5, 10 and 15 mg arms. "Not in table" means that label's table doesn't report it. Different populations; not a head-to-head comparison.
Stopping for side effects follows the same split. On Zepbound, 4.8%, 6.3% and 6.7% stopped at 5, 10 and 15 mg, against 3.4% on placebo; for digestive reasons alone, 1.9% to 4.3% against 0.5% [1]. On Mounjaro, 3.0% to 6.6% stopped for digestive reasons, against 0.4% [2]. For Zepbound's bowel effects in detail, see does Zepbound cause constipation?
Both labels say most nausea, vomiting and diarrhea came while the dose was rising
The majority of nausea, vomiting, and/or diarrhea events occurred during dose escalation and decreased over time.[1]
Mounjaro's label uses almost the same words [2]. Zepbound's adds when people tended to quit: "The majority of patients who discontinued ZEPBOUND due to adverse reactions did so during the first few months of treatment due to gastrointestinal adverse reactions" [1]. Neither label gives a number of days. The week-by-week picture for Zepbound is in Zepbound side effects.
Hair loss, low blood pressure, dry mouth and taste changes are on the Zepbound label at lower rates
- Hair loss: 7.1% of women and 0.5% of men on Zepbound, against 1.3% and 0% on placebo. The label links it to weight reduction, and no one on Zepbound stopped because of it.
- Low blood pressure: 1.6% against 0.1%, more often in people on blood pressure medicine (2.2%) and sometimes with dehydration.
- Faster heart rate: an average rise of 1 to 3 beats per minute on Zepbound, and 2 to 4 on Mounjaro.
- Dry mouth or throat: 1% against 0.1%.
- Taste changes (dysgeusia): 0.4% against 0%.
- Low blood sugar: 4.2% against 1.3% in Zepbound's diabetes trial, and 10.3% in people also taking a sulfonylurea.
All from the Zepbound label [1], except Mounjaro's heart-rate figure [2]. One thing people ask about isn't on either label: feeling cold. Neither label mentions cold or chills. For peeing more and dry mouth on Mounjaro, see does Mounjaro make you pee more?
The Warnings sections of both labels match closely
| Risk | Rate (label, which trials) | Signs the label lists | Zepbound § / Mounjaro § |
|---|---|---|---|
| Thyroid C-cell tumors | Seen in rats; unknown in people | Lump in the neck, trouble swallowing, shortness of breath, hoarseness | Boxed, 5.1 / Boxed, 5.1 |
| Acute pancreatitis | 0.23 vs 0.11 patients per 100 years (diabetes trials); 0.14 vs 0.15 (Zepbound weight trials) | Persistent or severe belly pain, sometimes into the back | 5.5 / 5.2 |
| Gallbladder inflammation (cholecystitis) | 0.7% vs 0.2% (Zepbound); gallbladder disease 0.6% vs 0% (Mounjaro) | Upper belly pain, fever, yellow skin or eyes, clay-colored stools | 5.4 / 5.8 |
| Kidney injury from dehydration | 0.5% vs 0.2% (Zepbound) | Follows vomiting, diarrhea or nausea that won't stop | 5.3 / 5.5 |
| Severe digestive reactions | 1.7–3.1% vs 1% (Zepbound) | Stomach problems that are severe or won't go away | 5.2 / 5.6 |
| Allergic reactions | Immediate reactions 2.1% vs 0.4%; severe 0.1% vs 0% (Zepbound) | Swelling of face or throat, trouble breathing, severe rash | 5.6 / 5.4 |
| Low blood sugar with insulin or a sulfonylurea | 10.3% with a sulfonylurea (Zepbound diabetes trial) | Shakiness, sweating, confusion, fast heartbeat | 5.7 / 5.3 |
| Eye complications in diabetes | Temporary worsening with rapid blood sugar improvement | Changes in vision | 5.8 / 5.7 |
| Food in the lungs under anesthesia | Rare postmarketing reports | Tell the surgical team you take it | 5.9 / 5.9 |
Zepbound and Mounjaro prescribing information, DailyMed version 40, August 2026. Both labels also say tirzepatide is not recommended for people with severe gastroparesis.
After approval, both labels add reports of hemorrhagic or necrotizing pancreatitis (sometimes fatal), ileus, intestinal obstruction, severe constipation including fecal impaction, anaphylaxis, angioedema, and acute kidney failure, sometimes needing dialysis [1] [2]. These come from voluntary reports, so their frequency is unknown. Whether Mounjaro suits someone with diabetes is covered in is Mounjaro safe?
In Mounjaro's heart-outcomes trial, side effects were similar to earlier trials, with some higher rates
SURPASS-CVOT compared Mounjaro (up to 15 mg) with dulaglutide, another GLP-1 drug, in 13,299 adults with type 2 diabetes and heart disease, over a median of about four years. Heart attack, stroke or heart-related death occurred in 12.1% on Mounjaro against 13.0% on dulaglutide (hazard ratio 0.92). That showed Mounjaro was not worse; it didn't prove it was better [2].
Side effects in that trial were similar to the earlier ones, with a few exceptions the label names: decreased appetite (17%), constipation (13%), vomiting (12%), abdominal pain (10%), fatigue (10%) and skin-sensation changes (0.7%) [2].
Tirzepatide can make birth-control pills less reliable for a few weeks at a time
Advise patients using oral hormonal contraceptives to switch to a non-oral contraceptive method, or add a barrier method of contraception for 4 weeks after initiation with ZEPBOUND and for 4 weeks after each dose escalation.[1]
Mounjaro's label says the same. The reason is slower stomach emptying, which the Zepbound label says is largest after the first dose and fades over time. Birth control that isn't taken by mouth isn't affected [1] [2].
On pregnancy, the labels differ because the uses differ. Zepbound's says weight loss "offers no benefit to a pregnant patient and may cause fetal harm" and to stop Zepbound when a pregnancy is recognized. Mounjaro's says human data are insufficient, animal studies showed reduced fetal growth, and poorly controlled diabetes in pregnancy carries its own risks [1] [2]. Plan this with your prescriber.
Compounded tirzepatide carries the label's drug risks, plus quality risks the brands don't
Compounded tirzepatide is not FDA-approved, and FDA does not review its safety, effectiveness or quality before it is sold [3]. The molecule's side effects above still apply. On top of them sit questions about what is in the vial.
| Question | Zepbound or Mounjaro | Compounded tirzepatide |
|---|---|---|
| Reviewed by FDA before sale? | Yes, approved with labels | No; not FDA-approved |
| Adverse-event reports | Collected through the labels' reporting lines | More than 730 reports to FDA as of May 31, 2026, likely underreported |
| Product quality evidence | Manufactured under FDA approval | A 2026 lab study by Eli Lilly scientists found a new impurity in tirzepatide plus vitamin B12 products; clinical effects unknown |
FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss; Jordan 2026 (all authors employed by Eli Lilly, which makes Zepbound and Mounjaro).
FDA notes it is "likely that adverse events from compounded versions of these drugs are underreported" [3]. The impurity study tested tirzepatide combined with B12 analogs bought on the US market; its authors, all Lilly employees, say the impurity's clinical effects are unknown [4]. For more, see is compounded tirzepatide safe?, our compounded tirzepatide guide and the starting dose of compounded tirzepatide. For how semaglutide compares, see Wegovy side effects.
See how the 88 compounded tirzepatide providers we score compare on monthly cost and care.