Saxenda vs Mounjaro in Australia

No randomised trial has compared liraglutide 3 mg with tirzepatide. Two searches of the trial literature on 6 October 2026 found none, and a Lilly-funded meta-analysis published in March 2026 says head-to-head comparisons are lacking.

SCALE Obesity and Prediabetes (NEJM 2015, Novo Nordisk-funded, 3,731 adults without diabetes, 56 weeks) tested liraglutide 3 mg daily. SURMOUNT-1 (NEJM 2022, Lilly-funded, 2,539 adults, 72 weeks) tested tirzepatide 5, 10 and 15 mg weekly. The figures sit side by side; they are not a comparison.

Liraglutide figures come from the Saxenda Product Information (revised 26 June 2026), still maintained and the Australian reference for liraglutide 3 mg; the generic brands carry the same indication wording. Mounjaro figures come from its Product Information revised 16 September 2026. Neither is the American label, which differs.

Gut effects are the common ones for both, mainly in the first weeks and after each dose step. In Saxenda's pooled trials, 39.3% had nausea against 13.8% on placebo, 20.9% diarrhoea (9.9%), 19.4% constipation (8.5%) and 15.7% vomiting (3.9%); 9.8% stopped because of adverse reactions against 4.3% on placebo. In Mounjaro's weight-management trials, nausea was 24.6% at 5 mg, 29.0% at 10 mg and 28.0% at 15 mg against 8.5% on placebo; diarrhoea 18.7% to 22.5% (7.8%); constipation 10.8% to 16.8% (5.2%); vomiting 8.3% to 12.5% (2.2%). Different trial pools of different lengths, not a head-to-head comparison.

Symptoms that need urgent medical attention, from the Mounjaro Consumer Medicine Information and the Saxenda Product Information: 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); sudden severe pain in the upper abdomen, fever or yellowing of the skin or eyes (gallbladder problems; gallstones occurred in 1.5% on Saxenda against 0.5% on placebo). Severe vomiting or diarrhoea can cause dehydration and kidney problems.

Both are Schedule 4 prescription-only medicines. Compounded versions have been illegal to make or supply in Australia since 1 October 2024, and 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 either. 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 prediabetes, high blood pressure, high cholesterol or sleep apnoea, alongside a reduced-energy diet and more physical activity. Whether a pharmacist may substitute a generic on a script written for Saxenda was not confirmed; a script naming liraglutide or the generic brand avoids the question.

Telehealth services (Juniper, Hims, Moshy, Mosh, Youly, hub.health, InstantScripts and others) sell a monthly bundle of consultations, medicine and delivery; the medicine and dose are decided at the consultation, not by the bundle price. In September 2026 Lilly opened LillyDirect, where a patient enters an e-script from their own doctor and a partner pharmacy dispenses and delivers Mounjaro; prices are shown only after the e-script token is entered.

On the evidence available, tirzepatide produces more weight loss than liraglutide: 20.9% at 15 mg over 72 weeks against 8.0% at 3 mg over 56 weeks in their own trials, and the independent BMJ analysis could not separate liraglutide from lifestyle treatment with confidence. Liraglutide costs about half as much a month at maintenance ($209.00 against $389.99 for the lowest Mounjaro maintenance dose on 9 November 2026), has three-year outcome data, and is a daily injection.

No Australian guideline covers switching from liraglutide to Mounjaro or back, and neither Product Information mentions it. The Saxenda document says liraglutide should not be used with any other GLP-1 receptor agonist and is not recommended with any other weight-loss medicine; the Mounjaro document is silent on combining. Novo Nordisk's only published advice to Saxenda prescribers, in its May 2025 letter, was to discuss alternatives including Wegovy 2.4 mg, with no dose mapping; no patient-facing notice was found.

The milligram figures are not equivalent: 3 mg of liraglutide a day is not 2.5 mg of tirzepatide a week. Each document gives one starting dose (liraglutide 0.6 mg daily, Mounjaro 2.5 mg weekly) and its own step-up schedule, with no shortcut for people arriving from another product, so a switch means repeating an escalation period and its side effects. Liraglutide has a half-life of 13 to 15 hours; tirzepatide is dosed weekly. British pharmacists writing in the Pharmaceutical Journal in 2025 describe the practice for a tirzepatide to semaglutide switch in the absence of official guidance: stop one, start the other at its starting dose on the next scheduled dose day, or after a one to two week washout if side effects were a problem, and titrate. That is practitioner practice for a different pair, not a guideline, and nothing equivalent has been published for liraglutide.

Weight regain after stopping is documented for both. In SCALE, people switched from liraglutide to placebo after 56 weeks regained 2.9% of body weight in 12 weeks. In SURMOUNT-4, people switched from tirzepatide to placebo regained 14% over a year while those who continued lost a further 5.5%. A BMJ meta-analysis of 37 studies (January 2026) put average regain after stopping any weight-loss medicine at 0.4 kg a month. Australian Prescriber, December 2025: when treatment is stopped, regaining weight is the norm.