Why two sets of numbersTirzepatide is sold as Mounjaro for type 2 diabetes and as Zepbound for weight management and sleep apnea. Each label reports side effects from its own trials, in different people and for different lengths of time, so the two columns below are not a head-to-head comparison.[1][2] For the Zepbound label alone, with a when-to-call-a-doctor table, see Zepbound side effects.
Side effects of tirzepatide in both labels
Both labels put stomach side effects at the top, and rates were higher in the weight trials than in the diabetes trials. Ranges cover the 5, 10 and 15 mg doses.
| Side effect | Zepbound 5–15 mg | Placebo | Mounjaro 5–15 mg | Placebo |
|---|---|---|---|---|
| Nausea | 25–29% | 8% | 12–18% | 4% |
| Diarrhea | 19–23% | 8% | 12–17% | 9% |
| Vomiting | 8–13% | 2% | 5–9% | 2% |
| Constipation | 11–17% | 5% | 6–7% | 1% |
| Abdominal pain | 9–10% | 5% | 5–6% | 4% |
| Dyspepsia (indigestion) | 9–10% | 4% | 5–8% | 3% |
| Decreased appetite | not in table | — | 5–11% | 1% |
| Fatigue | 5–7% | 3% | below 5% or not listed | — |
| Injection site reactions | 6–8% | 2% | below 5% or not listed | — |
| Hair loss | 4–5% | 1% | below 5% or not listed | — |
Zepbound figures pool SURMOUNT-1 and SURMOUNT-2 (up to 72 weeks, reactions in at least 2% of people); Mounjaro figures pool two placebo-controlled diabetes trials (reactions in at least 5%).[1][2] Stopping because of stomach side effects: 1.9–4.3% on Zepbound vs 0.5% placebo, and 3.0–6.6% on Mounjaro vs 0.4%.[1][2]
Nausea by dose: Zepbound vs Mounjaro
Nausea rose with dose on both labels but was about twice as common in the Zepbound weight trials as in the Mounjaro diabetes trials at every dose.[1][2]
Every rate on this page from both labels, plus the SURMOUNT-1 headache counts, is in one file: tirzepatide-side-effects.csv (label, trial pool, dose and source for each row).[1][2][9]
Mounjaro side effects in brief
Mounjaro's label reports milder stomach side effects than Zepbound's, from two placebo-controlled diabetes trials: nausea 12–18% versus 4%, diarrhea 12–17% versus 9%, and decreased appetite 5–11% versus 1%.[2]
- Low blood sugar: the main extra risk in diabetes is when Mounjaro is added to insulin or a sulfonylurea; the label says to consider lowering those doses.[2]
- Compared with semaglutide: SURPASS-2 tested Mounjaro against semaglutide 1 mg in type 2 diabetes; the efficacy results are on tirzepatide vs semaglutide.[8]
The full Mounjaro table, each symptom, the 4-year heart trial and the children's data are on Mounjaro side effects.
Does tirzepatide make you tired?
Some people do feel tired: fatigue was reported by 5%, 6% and 7% of people on Zepbound 5, 10 and 15 mg, against 3% on placebo.[1]
- 5%fatigue on 5 mg
- 7%fatigue on 15 mg
- 3%fatigue on placebo
- What “fatigue” includes: the label's fatigue figure also counts asthenia (weakness), lethargy and malaise.[1]
- Mounjaro: fatigue is not among the reactions its label lists at 5% or more in the diabetes trials.[2]
- Related label findings: dizziness (4–5% vs 2%) and low blood pressure (1–2% vs 0%) were more common on Zepbound, and the label links low blood pressure partly to stomach losses and dehydration.[1]
- Low blood sugar: with insulin or a sulfonylurea, tirzepatide can cause low blood sugar, whose listed symptoms include drowsiness and weakness.[1][2]
Does tirzepatide cause hair loss?
Hair loss is a listed side effect of Zepbound, reported by 4–5% of people versus 1% on placebo.[1] It was far more common in women (7.1%) than in men (0.5%), the label says it was associated with weight reduction, and no one on Zepbound stopped treatment because of it.[1] It does not appear in the Mounjaro table of reactions at 5% or more.[2] Details for women are on Zepbound side effects in females.
Does tirzepatide cause headaches?
Headache was about as common on tirzepatide as on placebo in SURMOUNT-1: 7.5%, 8.0% and 7.0% of people on 5, 10 and 15 mg, against 7.3% on placebo.[9] That is why headache is not in either label's table of side effects, which only lists reactions more common than with placebo.[1][2]
| Group | People with headache | Share |
|---|---|---|
| Placebo | 47 of 643 | 7.3% |
| Tirzepatide 5 mg | 47 of 630 | 7.5% |
| Tirzepatide 10 mg | 51 of 636 | 8.0% |
| Tirzepatide 15 mg | 44 of 630 | 7.0% |
The shares are computed from the posted counts.[9] The labels mention headache once, as a possible sign of low blood sugar, alongside dizziness, sweating and blurred vision; that risk applies mainly with insulin or a sulfonylurea.[1][2] By contrast, the label of Lilly's pill Foundayo does list headache, at 8–9% versus 7% on placebo.[10]
Tirzepatide constipation
Constipation affected 11–17% of people on Zepbound versus 5% on placebo, and 6–7% on Mounjaro versus 1%.[1][2] Unlike nausea and vomiting, it was most common at the lowest Zepbound dose: 17% on 5 mg, 14% on 10 mg and 11% on 15 mg.[1] Reports after approval added severe constipation, including fecal impaction, and intestinal obstruction to the label.[1]
New eye warning: NAION (November 2026)
On November 9, 2026, the FDA required every GLP-1 drug label, including Mounjaro and Zepbound, to add a warning about non-arteritic anterior ischemic optic neuropathy (NAION), a rare cause of sudden vision loss in one eye.[11]
| Evidence | Finding |
|---|---|
| Clinical trial meta-analysis (126 trials, 134,253 patients) | 15 probable NAION events: 6.4 per 100,000 person-years on GLP-1 drugs vs 3.8 on comparators |
| Usual rate in adults over 50 (published studies) | 2.3 to 10.2 cases per 100,000 people per year |
| FDA Sentinel study, type 2 diabetes, 2019–2024 | Hazard ratio 1.43 vs DPP-4 inhibitors (95% CI 1.02–2.01); 1.19 vs SGLT-2 inhibitors (not significant) |
| Animal studies | No mechanism found |
The FDA describes NAION as able to cause “acute, painless, decreased vision in one eye, including permanent vision loss,” and asks patients to contact a health care professional right away about sudden vision loss in one eye.[11] The communication covers the drug class and names no finding specific to tirzepatide; the Zepbound and Mounjaro labels cited on this page (August 2026) predate it, so the new wording will appear in later versions.[11][1][2]
Is tirzepatide safe?
Tirzepatide is FDA-approved, which means the FDA judged its benefits to outweigh its risks for the labeled uses, but it carries a boxed warning and several precautions.[1][2]
- Boxed warning: thyroid C-cell tumors in rats; human risk unknown; not for people with a personal or family history of medullary thyroid carcinoma or MEN 2.[1]
- Precautions in both labels: severe stomach reactions, kidney injury from dehydration, gallbladder disease, pancreatitis, serious allergic reactions, low blood sugar with insulin or sulfonylureas, diabetic eye disease, and aspiration under anesthesia.[1][2]
- Heart safety: in SURPASS-CVOT, 13,299 people with type 2 diabetes took tirzepatide or dulaglutide for a median of about 4 years; major cardiovascular events were not more frequent (hazard ratio 0.92), which met the test for non-inferiority, though superiority was not shown.[2][3]
- Compounded versions: unapproved tirzepatide is not reviewed by the FDA, which has received more than 730 adverse-event reports for compounded tirzepatide.[6]
Low blood sugar with tirzepatide
Low blood sugar is mainly a risk when tirzepatide is combined with insulin or a sulfonylurea. In the Zepbound trial in type 2 diabetes, blood sugar below 54 mg/dL occurred in 4.2% on tirzepatide versus 1.3% on placebo, and in 10.3% of those also taking a sulfonylurea.[1] The labels say to consider lowering the insulin or sulfonylurea dose when tirzepatide is started.[1][2]
Tirzepatide drug interactions
Because tirzepatide slows stomach emptying, it can change how some pills are absorbed.[1]
| Medicine | What the label says |
|---|---|
| Insulin or sulfonylureas | Consider a lower dose of these when starting, to reduce low blood sugar |
| Oral drugs with a narrow margin (e.g. warfarin) | Monitor when used together |
| Birth control pills | Switch to a non-oral method, or add a barrier method, for 4 weeks after starting and after each dose increase |
| Non-oral hormonal contraceptives | Should not be affected |
| Other GLP-1 drugs or tirzepatide products | Use together is not recommended |
If you take too much tirzepatide
The label says to contact the Poison Help Line (1-800-222-1222) or a medical toxicologist; care is supportive and may need a longer period of observation because of the roughly 5-day half-life.[1]
After stopping tirzepatide
The labels describe no withdrawal syndrome, but weight usually comes back: in SURMOUNT-4, people switched to placebo regained 14.0% of body weight in a year.[1][7] The drug itself clears over several weeks; see tirzepatide half-life.
When tirzepatide side effects happen
Most stomach side effects come during the weeks when the dose is being raised. The Zepbound label says most nausea, vomiting and diarrhea “occurred during dose escalation and decreased over time,” and the SURMOUNT-1 and SURMOUNT-5 papers describe the stomach effects as mostly mild to moderate.[1][4][5] The full timeline is on how long do Zepbound side effects last, and the dose steps on the tirzepatide dosage chart.
Related
- Zepbound side effectsFull label table and when to call a doctor
- Mounjaro side effectsThe diabetes label, symptom by symptom
- Tirzepatide vs semaglutideIncluding side effects in SURMOUNT-5
Frequently asked questions
What are the side effects of tirzepatide?
Does tirzepatide make you tired?
Fatigue was reported by 5–7% of people on Zepbound versus 3% on placebo; the label's figure includes weakness, lethargy and malaise.[1]
Does tirzepatide cause headaches?
Does tirzepatide cause hair loss?
Hair loss was reported in 4–5% of people on Zepbound versus 1% on placebo, mostly in women, and the label links it to weight reduction.[1]
What happens when you stop taking tirzepatide?
No withdrawal syndrome is described in the labels, but in SURMOUNT-4 people who stopped regained 14.0% of body weight over a year on average.[7]
Can tirzepatide affect your eyesight?
In November 2026 the FDA required all GLP-1 drug labels, including Mounjaro and Zepbound, to warn about NAION, a rare cause of sudden vision loss in one eye; trial data showed 6.4 versus 3.8 cases per 100,000 person-years. The labels already warn about worsening diabetic eye disease in type 2 diabetes.[11][1]
Sources
- Zepbound (tirzepatide) injection: prescribing information, Medication Guide and Instructions for Use
- Mounjaro (tirzepatide) injection: prescribing information and Instructions for Use
- FDA approves Lilly's Mounjaro to reduce cardiovascular risk in adults with type 2 diabetes
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)
- Aronne LJ et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5)
- FDA's concerns with unapproved GLP-1 drugs used for weight loss
- Aronne LJ et al. Continued treatment with tirzepatide for maintenance of weight reduction (SURMOUNT-4)
- Frías JP et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2)
- NCT04184622 (SURMOUNT-1) posted results: outcome measures and adverse events
- Foundayo (orforglipron) tablets: prescribing information
- FDA requires safety labeling changes for GLP-1 receptor agonists due to potential increased risk of rare but serious eye condition (NAION)