Wegovy vs Mounjaro in Australia

Until 2025, Mounjaro vs Wegovy comparisons, this page included, set one drug's placebo-controlled trial against the other's. SURMOUNT-5, published in the New England Journal of Medicine in May 2025, compared them directly.

It randomised 751 adults with obesity, or overweight with a weight-related condition, to the highest dose of each medicine they could tolerate for 72 weeks: tirzepatide 10 mg or 15 mg, or semaglutide 1.7 mg or 2.4 mg. Nobody had type 2 diabetes. Average starting weight was 113 kg, average BMI 39.4, two thirds were women, and the 32 sites were in the United States and Puerto Rico.

Both slow stomach emptying and act on appetite, and both carry the same family of side effects. The figures here come from the Australian Product Information for each medicine, the document the TGA approved, not from the American labels, which differ.

What to expect in the first months: Nausea, diarrhoea, constipation and vomiting are the common effects and they cluster around each dose increase. In Wegovy's pooled trials 38% of people had nausea against 14% on placebo, and 4.3% stopped because of gut effects. In Mounjaro's weight-management trials 25% to 29% had nausea depending on dose, against 8.5% on placebo. In the head-to-head trial, where both were pushed to the top dose, nausea was 44% in both groups. The Wegovy Product Information says to consider delaying the next dose step until symptoms improve. The Mounjaro document says to increase the dose only if needed and to consider a dose change or stopping if severe gut symptoms develop.

Symptoms that need urgent medical attention, listed in both Consumer Medicine Information leaflets: severe and persistent pain in the stomach or back, with or without vomiting (possible pancreatitis); swelling of the face, mouth or throat, hives or trouble breathing (allergic reaction); any sudden change in or loss of vision; and severe stomach pain with bloating, vomiting or constipation (bowel blockage). The Mounjaro leaflet also lists gallbladder problems: sudden severe pain in the upper abdomen, fever or yellowing of the skin or eyes. Severe vomiting or diarrhoea can cause dehydration and kidney problems, and both leaflets say to keep drinking fluids.

Both are Schedule 4 prescription-only medicines. Neither can be bought legally without a script, and compounded versions have been illegal to make or supply in Australia since 1 October 2024. In March 2026 the TGA reported that laboratory tests of imported unregistered products labelled as GLP-1 found they contained none.

A GP, a specialist or a nurse practitioner (within their scope of practice; rules vary by state and territory) can prescribe. The Product Information for both sets the same starting criteria: a BMI of 30 or more, or 27 to 30 with at least one weight-related condition such as high blood pressure, high cholesterol, sleep apnoea, heart disease or prediabetes, alongside a reduced-energy diet and more physical activity.

The telehealth services that advertise weight-loss programs (Juniper, Hims, Moshy, Mosh, Youly, hub.health, InstantScripts and others) sell a monthly bundle of consultations, medicine and delivery; which medicine and dose you get is decided at the consultation, not by the bundle price. In September 2026 Lilly opened LillyDirect, where you upload a script from your own doctor and a partner pharmacy dispenses and delivers Mounjaro. Lilly has not published its prices.

Tirzepatide produced more weight loss than semaglutide 2.4 mg in the only direct trial, by 6.5 percentage points on average, with similar nausea and fewer dropouts for side effects. That makes Mounjaro the more effective medicine for the average trial participant, and it is the more expensive one at every maintenance dose. Neither fact settles the choice for one person. A prescriber weighs the following.

No Australian guideline covers switching from Wegovy to Mounjaro or back. Neither Product Information mentions it. The Wegovy document says only that it should not be used together with another GLP-1 medicine, and that it has not been studied in people treated with other weight-management products.

Prescribers work from the dosing schedule of the new medicine. The milligram figures are not equivalent: 0.5 mg of Wegovy is not 5 mg of Mounjaro. Each document gives one starting dose for its own medicine (Wegovy 0.25 mg, Mounjaro 2.5 mg) with steps every four weeks, and neither gives a shortcut for people arriving from the other, so in practice a switch means repeating an escalation period and its side effects. British pharmacists writing in the Pharmaceutical Journal in 2025, on moving from tirzepatide to semaglutide, describe the same approach in the absence of any official guidance: stop one, wait the normal week (or one to two weeks if side effects were a problem), start the other at its starting dose and titrate. That is practitioner practice, not a guideline.

Weight regain after stopping either medicine is documented. A year after stopping semaglutide in the STEP 1 extension (an exploratory subset of 327 participants), people had regained two thirds of what they lost. In SURMOUNT-4, people switched from tirzepatide to placebo regained 14% of their body weight in a year while those who continued lost a further 5.5%.