Mounjaro side effects: what the Australian Product Information says.
Mounjaro (tirzepatide) is a once-weekly injection registered in Australia for type 2 diabetes, chronic weight management and obstructive sleep apnoea in adults with obesity. Like every medicine, it has side effects. This guide sets out what the TGA-approved Product Information (PI) and Consumer Medicine Information (CMI) list as common, less common and serious, when problems tend to appear, what to do and how to report them. It is general information, not medical advice.
The most frequent Mounjaro side effects are gastrointestinal: nausea, diarrhoea, vomiting, constipation, indigestion and reduced appetite. The PI describes them as mostly mild or moderate, most common while the dose is being stepped up, and decreasing over time. Less common but serious effects include acute pancreatitis, gallbladder disease, dehydration, severe allergic reactions, vision changes, and low blood sugar when combined with a sulfonylurea or insulin. Severe stomach pain that does not go away, facial swelling, trouble breathing or sudden vision loss need urgent care: call 000, or healthdirect on 1800 022 222 for 24-hour nurse advice.
- TGA registration. Type 2 diabetes in adults since 22 December 2022; chronic weight management (BMI 30 or above, or 27 to under 30 with a weight-related condition) since 9 September 2024; obstructive sleep apnoea in adults with obesity since 27 May 2025. Sources: TGA decisions for diabetes, weight and sleep apnoea.
- Current PI: vA13.0, September 2026, which also lists type 2 diabetes in children aged 10 and over weighing 50 kg or more. Source: TGA ARTG entry, PI and CMI downloads.
- Not PBS-listed for any indication. The PBAC recommended a type 2 diabetes listing in March 2026; in April 2026 the sponsor declined to proceed and the listing process ceased. Sources: PBS; RACGP newsGP, 28 April 2026.
- TGA safety updates: pulmonary aspiration under anaesthesia (3 June 2025); contraception advice for Mounjaro (1 December 2025); NAION, a rare optic nerve condition (23 July 2026).
- Supply and use. Pharmacy compounding of tirzepatide has not been permitted since 1 October 2024 (TGA); about 500,000 Australians used a GLP-1 medicine each month by April 2025 (UNSW, 31 July 2026).
The common side effects of Mounjaro.
The PI groups reactions by trial frequency: "very common" is at least 1 in 10, "common" 1 in 100 to 1 in 10. Nausea and diarrhoea were very common in every trial program; constipation, vomiting and abdominal pain were very common in the weight and sleep-apnoea trials. The table shows pooled SURMOUNT-1 and SURMOUNT-2 results (PI Table 4).
| Side effect | Tirzepatide, all doses (2,519 people) | Placebo (958 people) |
|---|---|---|
| Nausea | 27.5% | 8.5% |
| Diarrhoea | 20.9% | 7.8% |
| Constipation | 13.6% | 5.2% |
| Vomiting | 10.8% | 2.2% |
| Decreased appetite | 9.8% | 2.9% |
| Dyspepsia (indigestion) | 9.3% | 3.9% |
| Abdominal pain | 5.2% | 2.9% |
| Burping | 4.9% | 0.6% |
| Hair loss | 4.7% | 0.8% |
| Dizziness | 4.5% | 2.1% |
Diabetes-trial figures were lower: nausea 12.2, 15.4 and 18.3 per cent on 5, 10 and 15 mg versus 4.3 on placebo. Injection-site reactions (redness, bruising, itching, swelling or pain) are listed as common.
Less common effects listed in the PI.
PI Table 1 lists as common (1 to 10 per cent) bloating, burping, flatulence, reflux, fatigue, injection-site reactions, hypersensitivity, dizziness, hair loss and low blood pressure; the CMI adds heartburn, taste changes and unusual skin sensations. Uncommon (0.1 to 1 per cent): gallstones and acute pancreatitis. The KwikPen's benzyl alcohol preservative can also cause allergic reactions.
Serious side effects and the warnings behind them.
Listed as uncommon. The sign is severe stomach and back pain that does not go away, with or without vomiting. The PI says treatment stops if pancreatitis is suspected and is not restarted if confirmed.
Gallstones are uncommon; the CMI also warns of an inflamed gallbladder. Symptoms: sudden severe upper abdominal pain, fever, jaundice, clay-coloured stools.
Impaired gastric emptying, including severe gastroparesis, has been reported. The CMI lists intestinal slowing or blockage (severe abdominal pain, bloating, vomiting, constipation) as something to tell your doctor about promptly.
Vomiting and diarrhoea can cause dehydration, which the PI says may lead to deteriorating kidney function, including acute renal failure. Watch for a dry mouth, less or darker urine, headache, weakness and dizziness.
Very common when added to a sulfonylurea or insulin: clinically significant hypoglycaemia affected 10 to 14 per cent of people on a sulfonylurea and 14 to 19 per cent on basal insulin. The PI says reducing those medicines can lower the risk.
Hypersensitivity is common, and known hypersensitivity to tirzepatide or any excipient is the PI's only contraindication. Rash, hives, rapid swelling of the face, mouth or throat, or difficulty breathing or swallowing are emergency symptoms.
In July 2026 the TGA added a class-wide warning about NAION, a rare optic nerve condition that can cause permanent vision loss, advising urgent attention for sudden vision loss. Rapid glucose improvement can also temporarily worsen diabetic retinopathy.
A two-year rat study found more thyroid C-cell tumours at all doses; a six-month mouse study did not. The PI says the human relevance is unknown. The Australian CMI lists no thyroid contraindication; raise any family history of thyroid cancer with your prescriber.
The PI also warns about malnutrition, new or worsening depression or suicidal thoughts, pulmonary aspiration under anaesthesia or deep sedation, and pregnancy (Category D; stop at least one month before a planned pregnancy).
When side effects occur and how long they last.
The PI is specific: gastrointestinal reactions "occurred more often during dose escalation and decreased over time", and the delay in stomach emptying is "largest after the first dose". In pooled adult trials, 74 per cent of gastrointestinal reactions were mild and 23.3 per cent moderate. Because the dose steps up no sooner than every 4 weeks, symptoms often return briefly after each increase; see the Mounjaro doses guide.
Not everyone adapts: in the diabetes trials 3.0, 5.4 and 6.6 per cent of people on 5, 10 and 15 mg stopped because of a gastrointestinal event, against 0.4 per cent on placebo. The PI says the prescriber may consider dose modification or discontinuation; that decision is the prescriber's. See also Ozempic side effects.
Everyday side effects.
For nausea, diarrhoea, constipation, tiredness or injection-site reactions, the CMI says to speak to your doctor if they worry you. Keep drinking fluids, because dehydration is the path from a stomach upset to a kidney problem. If you have diabetes, carry glucose and know the signs of hypoglycaemia.
Do not stop the medicine or change the dose on your own: the CMI says not to stop without consulting your doctor and not to change your dose unless told to. Tell any doctor, surgeon, anaesthetist, pharmacist or nurse that you use Mounjaro.
When to seek help now.
The CMI says to call your doctor straight away or go to the nearest emergency department for symptoms of pancreatitis, an allergic reaction, gallbladder problems or changes to or loss of vision.
In an emergency call 000. For 24-hour advice from a registered nurse, call healthdirect on 1800 022 222. If you think you have injected too much, contact the Poisons Information Centre on 13 11 26, your doctor or an emergency department, even if you feel well.
Eating patterns people find easier on the gut.
The PI does not list any diet as a treatment for side effects. It does say reduced food intake is part of how the medicine works, and that malnutrition, including vitamin, mineral and protein deficiency, has been reported, so "balanced nutritional support should be considered".
Within that frame, the patterns people commonly find easier are smaller serves eaten slowly, a protein food first, fewer fatty or fried meals, fluids spread through the day, and plainer, cooler foods on nauseous days. Our guides cover the detail: what to eat on Mounjaro, foods for GLP-1 nausea, the GLP-1 portion guide and the tirzepatide food guide.
Reporting a side effect to the TGA.
The current CMI carries a black triangle: Mounjaro is "subject to additional monitoring due to approval of an extension of indications", and the TGA asks people to report side effects.
Report online through the TGA's adverse event form, by phone on 1300 633 424 (Monday to Friday, 9am to 5pm AEST), or through your doctor or pharmacist. You do not need to be certain the medicine caused the problem.
What are the most common side effects of Mounjaro?
The PI lists nausea and diarrhoea as very common (at least 1 in 10), with constipation, vomiting, abdominal pain, indigestion, reduced appetite, fatigue and injection-site reactions also frequent. In pooled weight-management trials, nausea affected 27.5 per cent on tirzepatide versus 8.5 per cent on placebo.
How long do Mounjaro side effects last?
The PI says gastrointestinal reactions were mostly mild or moderate, most frequent during dose escalation, and decreased over time. Severe, persistent or worsening symptoms should be discussed with the prescriber.
What are the serious side effects of Mounjaro?
Acute pancreatitis, gallbladder disease, intestinal blockage, dehydration leading to kidney injury, hypoglycaemia with a sulfonylurea or insulin, serious allergic reactions and vision changes. Persistent severe stomach pain, facial swelling, breathing difficulty or sudden vision loss need urgent care.
Does Mounjaro cause thyroid cancer?
A two-year rat study found more thyroid C-cell tumours; a mouse study did not. The PI says the human relevance is unknown, and the Australian CMI lists no thyroid contraindication. Raise any family history of thyroid cancer with your prescriber.
Can Mounjaro cause low blood sugar?
Alone, tirzepatide carries a low hypoglycaemia risk. Added to a sulfonylurea or insulin, clinically significant hypoglycaemia affected 10 to 14 and 14 to 19 per cent of trial participants respectively; the PI says the prescriber may reduce those medicines.
What should I do if I have side effects from Mounjaro?
For less serious effects, speak to your doctor if they worry you. For signs of pancreatitis, gallbladder disease, allergic reaction or vision loss, call your doctor straight away or go to an emergency department; call 000 in an emergency. Never stop or change the dose without your prescriber.
How do I report a Mounjaro side effect in Australia?
Use the TGA's online adverse event form, call 1300 633 424 (Monday to Friday, 9am to 5pm AEST), or ask your doctor or pharmacist to report. You do not need to be certain the medicine caused the problem.
Primary sources checked for this page.
- TGA ARTG entry 439692: current Mounjaro PI (vA13.0, September 2026) and CMI.
- TGA: Mounjaro Product Information, 2024 AusPAR attachment.
- TGA safety update: pulmonary aspiration, 3 June 2025.
- TGA safety update: NAION, 23 July 2026.
- TGA safety update: contraception advice, 1 December 2025.
- TGA: reporting adverse events for consumers.
- Jastreboff et al., SURMOUNT-1, NEJM 2022.
- PBS: tirzepatide medicine status.
Editorial method: primary Australian regulatory sources (TGA-approved PI and CMI, TGA safety updates and registration decisions, PBS records) were checked first, peer-reviewed trial publications second. Clinical review by a named Australian health professional is pending. See the Preptide editorial policy.
Important: General information only, not medical advice. Mounjaro is a registered trademark of Eli Lilly; Preptide is independent and is not affiliated with, endorsed by or sponsored by Eli Lilly. Preptide is food, not medication, and does not prescribe, sell, recommend or promote prescription medicines. Talk to your doctor or pharmacist about any medicine. In an emergency call 000. Read our editorial policy and Health Acknowledgement.