The most common side effects of Mounjaro (tirzepatide) are digestive: nausea, diarrhoea, vomiting and constipation. In the weight-loss trials behind the US label, nausea affected 25% to 29% of adults against 8% on placebo, mostly while the dose was being stepped up (US label). Singapore's public product page does not print the side-effect section (NDF), so these figures come from the US and European labels. At GetLean, daily WhatsApp coaching means anything clinical can reach Dr Quek early.
Availability in Singapore. This medicine is registered with Singapore's Health Sciences Authority, and its registered indication includes weight management. Which medicine suits a particular person, if any does, is decided by the doctor who assesses them.
What are the most common side effects of Mounjaro?
The most common side effects of Mounjaro are digestive: in the US label's pooled weight-loss trials, nausea, diarrhoea, vomiting, constipation, stomach pain and indigestion each affected between 8% and 29% of adults on tirzepatide, against 2% to 8% on placebo. The label lists 16 reactions reported by at least 2% of adults on tirzepatide and more often than on placebo, from two placebo-controlled trials in 2,519 adults treated for up to 72 weeks (US label).
The share of adults reporting each reaction in the US label's pooled weight-loss trials.
| Reported by adults in the trials | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 8% | 25% | 29% | 28% |
| Diarrhoea | 8% | 19% | 21% | 23% |
| Vomiting | 2% | 8% | 11% | 13% |
| Constipation | 5% | 17% | 14% | 11% |
| Stomach pain | 5% | 9% | 9% | 10% |
| Indigestion | 4% | 9% | 9% | 10% |
| Injection-site reactions | 2% | 6% | 8% | 8% |
| Tiredness | 3% | 5% | 6% | 7% |
| Allergic reactions | 3% | 5% | 5% | 5% |
| Burping | 1% | 4% | 5% | 5% |
| Hair loss | 1% | 5% | 4% | 5% |
| Reflux | 2% | 4% | 4% | 5% |
| Wind | 2% | 3% | 3% | 4% |
| Bloating | 2% | 3% | 3% | 4% |
| Dizziness | 2% | 4% | 5% | 4% |
| Low blood pressure | 0% | 1% | 1% | 2% |
The doses in the table are the trials' arms, not a guide to anyone's dose: which dose suits a person is the prescribing doctor's decision. Digestive side effects of any kind were reported by 56% of adults at each tirzepatide dose, against 30% on placebo (US label).
The European label shows the same pattern in its weight-management trial in adults without type 2 diabetes: nausea in 24.6%, 33.3% and 31.0% at 5, 10 and 15 mg against 9.5% on placebo, and diarrhoea in 18.7%, 21.2% and 23.0% against 7.3%, with most of these digestive reactions mild (60.8%) or moderate (34.6%). It classes nausea, diarrhoea, vomiting, stomach pain and constipation as very common in the weight-management trials, meaning at least 1 in 10 people, and gallstones, gallbladder inflammation and acute pancreatitis as uncommon, between 1 in 1,000 and 1 in 100 (EU label).
How long do Mounjaro side effects last?
Mounjaro's digestive side effects mostly come while the dose is being raised and ease over time: the US label says the majority of nausea, vomiting and diarrhoea events occurred during dose escalation and decreased over time (US label), and the European label says their incidence was higher during dose escalation and decreased over time (EU label). Neither the US nor the European label gives a number of days or weeks. In SURMOUNT-1, the main weight-loss trial, most digestive events were mild to moderate and occurred primarily during dose escalation (Jastreboff 2022).
The dose steps are where this shows. In Singapore's product information, the starting dose of tirzepatide is 2.5 mg once weekly, raised to 5 mg after 4 weeks, with any further increase in 2.5 mg steps after at least 4 weeks on the current dose (NDF).
When side effects did stop treatment, it was usually early. In the US label's trials, 4.8% to 6.7% of adults on tirzepatide stopped because of side effects, against 3.4% on placebo, and the majority who stopped did so during the first few months of treatment, because of digestive side effects (US label).
What are the worst side effects of taking Mounjaro?
The worst side effects of Mounjaro are the uncommon serious ones in its labels' warnings: severe digestive reactions, acute pancreatitis, gallbladder disease, kidney injury from dehydration and serious allergic reactions. The US label's figures, from its pooled weight-loss trials unless stated (US label):
- Severe stomach and bowel reactions: 1.7%, 2.5% and 3.1% of adults at 5, 10 and 15 mg, against 1% on placebo.
- Acute pancreatitis: confirmed in 0.2% of adults on tirzepatide and 0.2% on placebo. The label adds that fatal and non-fatal cases have been observed in people treated with GLP-1 medicines, tirzepatide included.
- Gallbladder disease: gallstones in 1.1% against 1%, gallbladder inflammation in 0.7% against 0.2%, and gallbladder removal in 0.2% against none.
- Kidney injury from dehydration: 0.5% against 0.2%. Since approval there have been reports of acute kidney injury, in some cases needing dialysis, mostly in people who had become dehydrated from nausea, vomiting or diarrhoea.
- Serious allergic reactions: severe in 0.1% against none in the trials, and anaphylaxis and swelling of the face and throat (angioedema) have been reported since approval.
- Low blood sugar in people with type 2 diabetes: in the trial in adults with type 2 diabetes, 4.2% of those on tirzepatide against 1.3% on placebo; among those on tirzepatide, 10.3% of people also taking a sulfonylurea against 2.1% of those not taking one.
- Problems under anaesthesia: rare reports of food or liquid entering the lungs during anaesthesia or deep sedation in people on GLP-1 medicines, because the stomach empties more slowly.
In rats, tirzepatide caused thyroid C-cell tumours, and whether it does so in people is not known; the US label rules it out for anyone with a personal or family history of medullary thyroid carcinoma or MEN 2 (US label). The European label records the same rat finding as of unknown human relevance and lists hypersensitivity as its only contraindication (EU label), as Singapore's product page does (NDF).
When should you call a doctor about Mounjaro side effects?
Call a doctor straight away about severe stomach pain that will not go away, signs of a serious allergic reaction, or nausea, vomiting or diarrhoea that does not settle. These are the side effects the US Medication Guide singles out (US Medication Guide):
- Severe pain in the stomach area that will not go away, with or without nausea or vomiting, sometimes felt through to the back: the guide says to stop using the medicine and call the doctor right away, because it can be pancreatitis.
- Pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-coloured stools: possible gallbladder problems.
- Swelling of the face, lips, tongue or throat, problems breathing or swallowing, severe rash or itching, fainting or dizziness, or a very rapid heartbeat: the guide says to stop and get medical help right away.
- Nausea, vomiting or diarrhoea that does not go away: the fluid loss can lead to kidney problems, and the guide says it is important to drink fluids.
- A lump or swelling in the neck, hoarseness, trouble swallowing or shortness of breath: symptoms the guide asks people to report because of the thyroid warning.
The guide also asks people to talk to their healthcare provider about any side effect that bothers them or does not go away. Any change to a prescribed dose is a decision for the prescribing doctor.
Side effects are why daily contact matters: at GetLean, daily WhatsApp coaching keeps you in touch with our care team (9am to 9pm every day, Singapore time), so anything clinical can reach Dr Quek early, not weeks later. Outside those hours an urgent symptom does not wait for a reply: go to an emergency department, or call 995 if it is an emergency.
What should I avoid while taking Mounjaro?
While taking Mounjaro, the labels say to avoid using it with another tirzepatide product or any other GLP-1 medicine, to avoid becoming dehydrated, and to tell every doctor before an operation or sedation (US Medication Guide). Item by item:
- Other GLP-1 medicines: the US Medication Guide says tirzepatide should not be used with other tirzepatide-containing products or any GLP-1 receptor agonist medicines.
- Dehydration: the guide says it is important to drink fluids, and the European label advises precautions to avoid fluid depletion and electrolyte disturbances, particularly in older people (EU label).
- Surgery and sedation: tell every doctor before a planned operation or procedure under anaesthesia or deep sedation.
- The contraceptive pill: the US label advises switching to a non-oral method, or adding a barrier method, for 4 weeks after the first dose and for 4 weeks after each dose increase (US label), while the European label, from a study of a single dose, concludes that no adjustment of oral contraceptives is required (EU label). The two labels advise differently, so this is one to raise with the prescribing doctor.
- Pregnancy: the European label says to stop tirzepatide at least 1 month before a planned pregnancy; the US label gives no pre-conception window (pregnancy sections).
- Diabetes medicines: tell the doctor about insulin or a sulfonylurea, because of the low blood sugar risk above.
Food and alcohol are not on the labels' list. The US labels list no foods to avoid and say the injection can be taken with or without meals (US labels), and they carry no alcohol-specific warning (US labels), which is not the same as saying alcohol is safe. Managing nausea on GLP-1 goes through the food lists against the label, and alcohol on GLP-1 covers drinking.
Does Mounjaro cause hair loss?
Mounjaro can cause hair loss in some people: in the US label's weight-loss trials, 4% to 5% of adults on tirzepatide reported it against 1% on placebo, far more often women (7.1%) than men (0.5%). The label links it to weight reduction, and no one on tirzepatide stopped treatment because of it (US label). The European label classes hair loss as common, meaning between 1 in 100 and 1 in 10 people (EU label). Hair shedding on GLP-1 covers what it looks like and how long it lasts.
Do Mounjaro injections hurt?
The labels do not measure pain from a Mounjaro injection; they count injection-site reactions, which 6% to 8% of adults on tirzepatide reported in the US weight-loss trials, against 2% on placebo (US label). That group includes bruising, redness, itching, pain and rash where the needle went in. The European label reports 8.0% against 1.8% in its weight-management trials, and across its phase 3 trials the reactions were at worst mild for 91% of people who had one and moderate for 9%, with none serious (EU label). In the US trials, injection-site reactions were more common in people who developed antibodies to tirzepatide (11.3%) than in those who did not (1%) (US label).
Singapore's product information has the injection given under the skin of the abdomen or thigh, or by another person into the back of the upper arm, with the site rotated at each dose (NDF). Bruises, marks and lumps covers what is ordinary at the injection site and what is not.
Are Mounjaro side effects different with type 2 diabetes?
The same digestive side effects lead with type 2 diabetes, and they were less frequent in the European label's diabetes trials: nausea affected 12.2%, 15.4% and 18.3% of adults at 5, 10 and 15 mg against 4.3% on placebo, and diarrhoea 11.8%, 13.3% and 16.2% against 8.9% (EU label).
The difference that matters is low blood sugar when tirzepatide is taken with insulin or a sulfonylurea. The European label reports clinically significant low blood sugar in 10% to 14% of people when tirzepatide was added to a sulfonylurea and in 14% to 19% when it was added to basal insulin (EU label), and the US Medication Guide asks people on either to tell their doctor before using it (US Medication Guide).
What are the long-term effects of Mounjaro?
In the US label's weight-loss trials, which treated adults for up to 72 weeks and, in a later trial, for up to 88 weeks, Mounjaro's side effects stayed the same kind: the adverse reactions in the later trial were similar (US label). The European label's side-effect table also draws on SURPASS-CVOT, which followed 13,299 adults with type 2 diabetes and cardiovascular disease for a median of 4 years against dulaglutide (EU label). What is not known is whether the thyroid tumours tirzepatide caused in rats apply to people (US label). Long-term effects of GLP-1 sets out what the longest trials of the whole class show.
What does GetLean do about side effects on Mounjaro?
At GetLean, anything clinical you raise on daily WhatsApp coaching goes to Dr Quek, and he reviews how it is going every month, with dose changes made at that check-in, towards the lowest effective dose. Mounjaro at GetLean is from S$488 a month (S$788 depending on dose, S$1,088 at the max dose), all-in: Dr Quek's video consultations and reviews, the medication delivered to you, and daily WhatsApp coaching. Mounjaro in Singapore has the price for each dose.
The first step is a 30-minute video consultation with Dr Quek for S$20, refunded in full if he decides medication is not right for you, and a consultation does not guarantee a prescription. Wegovy side effects has the equivalent figures for semaglutide, and GLP-1 side effects sorts the class by how serious each effect is.
Book your consult with Dr Quek.
Read the transcript
What are the side effects of Mounjaro, or tirzepatide?
Mostly digestive: nausea, diarrhoea, vomiting and constipation. They mostly come while the dose is going up.
I'm Dr Quek, a Singapore-registered doctor, and the doctor behind the GetLean GLP-1 Taper Plan.
How common is nausea?
In the weight-loss trials, up to twenty-nine in every hundred people on Mounjaro reported it, against eight on placebo, a dummy injection.
Most people did not stop because of side effects.
In the big trial, most of the digestive side effects were mild to moderate.
How long do the side effects last?
There's no set number of days, and the label gives no timeframe. In the trials, most of the nausea, vomiting and diarrhoea eased over time.
If they don't ease, or they're back after a step up, tell us, and don't just push through.
What helps with the nausea?
These are the usual tips, and they're low-risk. Eat smaller meals, eat slowly, go easy on fatty and spicy food, especially around injection day, and don't lie down straight after eating.
Think plain porridge, not a spicy laksa.
What about hair loss and tiredness?
Tiredness, hair loss, dizziness and reactions where you inject, like redness, itching or bruising, were all reported more often than on placebo.
Hair loss was reported by up to five in every hundred on Mounjaro, against one on placebo. It's linked to the weight loss itself.
When should you call a doctor?
Mild nausea or loose motion in the weeks after a dose goes up is common, and on its own it's not an emergency.
But severe stomach pain that won't go away, or swelling of your face, lips, tongue or throat, means stop the injection and get medical help right away.
Vomiting or diarrhoea that won't stop, or you can't keep fluids down, needs a doctor right away too, and in an emergency, go to A and E or call nine nine five.
If you're considering GLP-1 medication to reach your weight goal, and you'd like to taper off it one day, I invite you to visit getleanclinic.sg to learn about our approach and the GetLean GLP-1 Taper Plan.
Common questions
What are the side effects of Mounjaro?
The most common side effects of Mounjaro (tirzepatide) are digestive: nausea, diarrhoea, vomiting, constipation, stomach pain and indigestion. In the weight-loss trials behind the US label, nausea affected 25% to 29% of adults on tirzepatide against 8% on placebo, and the majority of nausea, vomiting and diarrhoea events occurred during dose escalation and decreased over time (US label).
How long do Mounjaro side effects last?
Mounjaro's digestive side effects mostly come while the dose is being raised and ease over time: the US label says the majority of nausea, vomiting and diarrhoea events occurred during dose escalation and decreased over time (US label). Neither the US nor the European label gives a number of days or weeks. When side effects did stop treatment in the trials, the majority who stopped did so during the first few months.
What are the worst side effects of taking Mounjaro?
The worst side effects of Mounjaro are the uncommon serious ones in its labels' warnings: severe digestive reactions, acute pancreatitis, gallbladder disease, kidney injury from dehydration and serious allergic reactions. In the US label's weight-loss trials, severe digestive reactions affected 1.7% to 3.1% of adults on tirzepatide against 1% on placebo, and gallbladder inflammation 0.7% against 0.2% (US label).
What if Mounjaro side effects start and my next appointment is months away?
Talk to the prescribing doctor about any side effect that bothers you or does not go away, as the US Medication Guide asks, without waiting for the next scheduled appointment, and do not change the dose yourself (US Medication Guide). Severe stomach pain that will not go away, or signs of a serious allergic reaction, need help right away. At GetLean, daily WhatsApp coaching keeps you in touch with the care team (9am to 9pm every day, Singapore time), so anything clinical can reach Dr Quek early, and Dr Quek decides any dose change. Outside those hours an urgent symptom does not wait for a reply: go to an emergency department, or call 995 if it is an emergency.
What should I avoid while taking Mounjaro?
While taking Mounjaro, the labels say to avoid using it with another tirzepatide product or any other GLP-1 medicine, to avoid becoming dehydrated, and to tell every doctor before an operation or sedation (US Medication Guide). The US labels list no foods to avoid (US labels). Anyone on the contraceptive pill should ask the prescribing doctor about it, because the US and European labels advise differently.
Does Mounjaro cause hair loss?
Mounjaro can cause hair loss in some people: in the US label's weight-loss trials, 4% to 5% of adults on tirzepatide reported it against 1% on placebo, far more often women (7.1%) than men (0.5%) (US label). The label links it to weight reduction, and no one on tirzepatide stopped treatment because of it.
Do Mounjaro injections hurt?
The labels do not measure pain from a Mounjaro injection; they count injection-site reactions, which 6% to 8% of adults on tirzepatide reported in the US weight-loss trials, against 2% on placebo (US label). The European label reports 8.0% against 1.8% in its weight-management trials, and across its phase 3 trials the reactions were at worst mild for 91% of people who had one, with none serious (EU label).
What are the long-term effects of Mounjaro?
In the US label's weight-loss trials, which treated adults for up to 72 weeks and, in a later trial, for up to 88 weeks, Mounjaro's side effects stayed the same kind: the adverse reactions in the later trial were similar (US label). The European label also draws on SURPASS-CVOT, which followed adults with type 2 diabetes and cardiovascular disease for a median of 4 years (EU label). What is not known is whether the thyroid tumours tirzepatide caused in rats apply to people (US label).