Mounjaro side effects, by the numbers

The most common Mounjaro side effects

These are the side effects on Mounjaro's label, from two placebo-controlled trials in adults with type 2 diabetes (SURPASS-1 and SURPASS-5), in which 718 people took Mounjaro for an average of 36.6 weeks.¹ Each figure is the share of people who reported the effect at least once.

Source: Mounjaro prescribing information, Table 1; the last three rows come from the text of the same section.¹ Across all stomach side effects, 37.1–43.6% of people on Mounjaro reported at least one, against 20.4% on placebo.¹ The dose columns are trial groups, not a suggestion of which dose suits you.

Tirzepatide side effects in the weight-management trials

If you take Mounjaro for weight loss, as people in the UK can, tirzepatide's weight-management trials are the closer match.⁸ In the US the same medicine is sold for weight management as Zepbound (see Mounjaro vs Zepbound), and its label pools SURMOUNT-1, in adults without diabetes, and SURMOUNT-2, in adults with type 2 diabetes: 2,519 adults treated for up to 72 weeks.²

Stomach side effects were more common here: 56% of people on each dose had at least one, against 30% on placebo.² The two sets of trials differed in who took part and for how long, so read the tables separately, not as a head-to-head.

Weight-management trials (SURMOUNT-1 and SURMOUNT-2)

Source: Zepbound prescribing information, Table 1 (reactions in at least 2% of people and more common than on placebo).² The full list is on our Zepbound side effects page.

When Mounjaro side effects happen, and when they ease

The label gives no day-by-day timeline, and nobody can predict yours. It does describe a pattern.

1. While the dose is stepped up
   When most reports came

   Labels start tirzepatide low and step it up gradually; your prescriber sets the steps. Most reports of nausea, vomiting and diarrhea came during this escalation,¹ and in SURMOUNT-5 most stomach side effects on tirzepatide were mild to moderate.³

2. After each change
   Worth writing down

   The weeks after a change are the ones most worth noting: how you felt, and what you managed to eat and drink.

3. The months that follow
   Usually easing

   Those reports decreased over time.¹ In the weight-management trials, most people who stopped because of side effects did so in the first few months.²

4. If it doesn't settle
   Tell your care team

   The Medication Guide asks you to tell your healthcare provider about stomach problems that are severe or won't go away, and to tell them right away about nausea, vomiting or diarrhea that doesn't go away.¹

Common side effects, one by one: what helps and when to call

General, non-drug measures only (the figures are in the tables above). The NHS says a pharmacist or doctor may be able to advise on reducing side effects that bother you or don't go away,¹² and none of this replaces advice from your prescriber.

Nausea

Nausea, a queasy, unsettled stomach, was the most reported side effect in both sets of trials.^1,2 What may help: drinking fluids, which the Medication Guide says helps reduce your chance of dehydration,¹ and avoiding alcohol, which the NHS says can increase nausea and vomiting.¹² Ask your care team whether changing what or how much you eat might help. Our guide to what to eat on Mounjaro sets out what Lilly and the NHS suggest for nausea. Call your care team if nausea stops you eating or drinking, or doesn't go away.

Diarrhea

What may help: keep drinking. The Medication Guide says fluids help reduce your chance of dehydration, which can lead to kidney problems.¹ Call your care team right away if diarrhea doesn't go away.

Constipation

What may help: ask your care team whether more fiber and fluids would suit you. Call your care team if constipation is severe or won't go away; severe constipation, including fecal impaction, and bowel blockage have been reported since the medicine was approved.¹

Vomiting

What may help: avoiding alcohol, which the NHS says can increase vomiting,¹² and asking your care team how best to keep fluids up. Call your care team right away if vomiting doesn't stop or you can't keep fluids down.

Indigestion, reflux and burping

What may help: ask your care team whether changes to your meals might help. Call your care team if symptoms are severe or won't go away.

Decreased appetite

Partly how the medicine works: the Zepbound label describes GLP-1 as a natural regulator of appetite and calorie intake.² It still matters if eating less means too little food or fluid, and a simple food and drink record makes that easy to show your care team.

Stomach pain

Mild discomfort is one thing; severe pain that won't go away is a red flag, covered below.

Less talked-about Mounjaro side effects

These come up often in searches. Here is what the labels and trials say.

• Hair loss. In the weight-management trials, hair loss was reported by 4–5% of people on tirzepatide against 1% on placebo: 7.1% of women and 0.5% of men.² The Zepbound label links it with weight reduction, and no one on tirzepatide in those trials stopped because of it. Mounjaro's own label lists it among reports since approval.¹
• Burping and "sulfur burps". The label records burping (eructation): 2.5–3.3% against 0.4% in the diabetes trials, and 4–5% against 1% in the weight-management trials.^1,2 It says nothing about smell; "sulfur burps" is not a label term.
• Tiredness. Fatigue was reported by 5–7% of people on tirzepatide against 3% on placebo in the weight-management trials,² and by 10% of people on Mounjaro in a heart-outcomes trial with a median follow-up of about four years.¹
• Headache. Headache isn't in either tirzepatide label's table of common side effects.^1,2 The Medication Guide does list it among possible signs of low blood sugar, a risk mainly when Mounjaro is used with insulin or a sulfonylurea.¹
• Injection-site reactions. Reactions where you inject were reported by 3.2% of people on Mounjaro against 0.4% on placebo in the diabetes trials, and by 6–8% against 2% in the weight-management trials.^1,2 The label asks you to rotate injection sites with each dose; our guide to Mounjaro injection sites explains how.
• Dizziness and low blood pressure. In the weight-management trials, dizziness affected 4–5% of people on tirzepatide against 2% on placebo, and low blood pressure 1.6% against 0.1%.²
• Eyes. Mounjaro's label warns about complications in people with a history of diabetic retinopathy and asks you to report changes in vision.¹ NAION, an eye condition that Europe's regulator lists as a very rare side effect of semaglutide, is not in the US tirzepatide labels,^1,2 and the European review did not cover tirzepatide.⁷
• "Ozempic face". Not a label term: it isn't in Mounjaro's label. It's an informal name for loss of fullness in the face with rapid weight loss; Harvard Health notes it can follow any GLP-1 medicine or any other cause of rapid weight loss.⁵
• Muscle and lean mass. The Zepbound label says tirzepatide lowers weight with greater fat loss than lean-mass loss.² In a SURMOUNT-1 body-scan substudy of 160 people, about 75% of the weight lost was fat and 25% lean mass, in both the tirzepatide and placebo groups.⁴ Lean mass, as a scan measures it, is not the same thing as muscle.

Serious side effects of Mounjaro

Serious side effects are less common, and most have warning signs worth learning. These are the label's main warnings.

Pancreatitis figures count people whose pancreatitis was confirmed on expert review across Mounjaro's clinical studies.¹

Who should not take Mounjaro

Mounjaro has a boxed warning: in rats, tirzepatide caused thyroid C-cell tumors, and it is not known whether it causes these tumors, including medullary thyroid carcinoma (MTC), in people.¹ The label says not to use Mounjaro if you or anyone in your family has had MTC, if you have multiple endocrine neoplasia syndrome type 2 (MEN 2), or if you've had a serious allergic reaction to tirzepatide or any of its ingredients.¹

Tell your healthcare provider about a lump or swelling in your neck, hoarseness, trouble swallowing or shortness of breath, which the Medication Guide lists as possible symptoms of thyroid cancer.¹ The label also says Mounjaro is not recommended for people with severe gastroparesis (very slow stomach emptying), and asks you to mention pancreas problems, diabetic retinopathy and planned surgery before you start.¹

Side effects in children 10 and older

In the US, Mounjaro is approved for type 2 diabetes in children aged 10 and older.¹ In the children's trial, vomiting (16% and 12% on the two doses, against 3% on placebo), stomach pain (22% and 15%, against 9%) and low blood sugar were more common than in adults.¹ The label says the KwikPen isn't recommended for children to use on themselves.¹

Mounjaro side effects in women: contraception, pregnancy and hair loss

The only side effect the labels break down by sex is hair loss: 7.1% of women on tirzepatide against 0.5% of men in the weight-management trials, and 1.3% and 0% on placebo.²

Mounjaro can make birth control pills taken by mouth work less well. The label advises switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase.¹ The UK's MHRA gives the same advice for Mounjaro, and says GLP-1 medicines should not be taken during pregnancy, while trying to get pregnant or while breastfeeding.¹¹

If you're planning a pregnancy, plan this with your prescriber: the same MHRA guidance lists a gap of at least one month between stopping tirzepatide and trying to get pregnant.¹¹ Our Mounjaro half-life guide sets out what the labels and the MHRA say about planning a pregnancy.

Long-term Mounjaro side effects, and stopping

The longest look comes from SURPASS-CVOT, a heart-outcomes trial that followed 13,299 adults with type 2 diabetes and established cardiovascular disease for a median of 210 weeks, about four years, with 6,647 of them on Mounjaro.¹ The label says side effects were similar to the shorter trials, with exceptions it lists: decreased appetite (17%), constipation (13%), vomiting (12%), stomach pain (10%), fatigue (10%) and unusual skin sensations (0.7%).¹

Stopping is a decision to make with your prescriber. In SURMOUNT-4, adults who had taken tirzepatide for 36 weeks were either kept on it or switched to placebo: over the next year, weight rose by an average of 14.0% on placebo, while those who continued lost a further 5.5%.² Regain after stopping is a signal worth discussing, not a personal failure.

Mounjaro jab side effects in the UK

In the UK, Mounjaro is the brand for both type 2 diabetes and weight management; the MHRA authorised the weight-management use in November 2023.⁸ It is the same medicine, so if you use the jab for weight loss, the weight-management trial figures above are the closest guide.

On the NHS in England, NICE recommends tirzepatide for adults with a BMI of at least 35 (usually 2.5 lower for people from some ethnic backgrounds) and at least one weight-related condition. NHS England is rolling it out in phases, starting with people who have a BMI of 40 or more and at least four of five listed conditions, with more groups from around June 2026 and March 2027.⁹

In January 2026 the MHRA updated its warnings about a small risk of severe acute pancreatitis with all GLP-1 and dual GIP/GLP-1 medicines, including Mounjaro.¹⁰ If you think you've had a side effect, you can report it to the MHRA's Yellow Card scheme.¹⁰ Tracking a weekly jab? See our weight-loss injection tracker guide, or compare Mounjaro vs Wegovy.

Keeping a record your prescriber can use

A record beats memory at an appointment: the dose you took and when, how you felt each day, what you ate and drank, and anything that changed, such as a new strength or a new medicine. Handle keeps it for free, whichever tirzepatide brand you use; see the Mounjaro tracker and tirzepatide tracker guides, or the GLP-1 side effect tracker checklist.

Questions to ask your prescriber about side effects

Side effects are easier to handle with a plan agreed in advance. These are good questions to bring.

1. Which side effects should I call you about, and which can I manage at home?
2. What should I do if I can't keep fluids down?
3. Do my other medicines, such as insulin, a sulfonylurea or the contraceptive pill, need any changes while I'm on Mounjaro?
4. What should I do if I miss a dose? Mounjaro's instructions have their own rule, so it's worth asking rather than guessing.
5. I have a procedure coming up. Who needs to know that I take Mounjaro?

For how tirzepatide's side effects compare with semaglutide's, see semaglutide vs tirzepatide and Mounjaro vs Ozempic, or our overview of GLP-1 side effects.