Tirzepatide

Tirzepatide (Mounjaro) is a TGA-registered, prescription-only dual GIP/GLP-1 receptor agonist approved for type 2 diabetes and chronic weight management. SURMOUNT trials showed average weight loss of roughly 13–23%.

What it is

Tirzepatide is a dual GIP and GLP-1 receptor agonist — it acts on two gut-hormone pathways rather than one. In Australia it is sold as Mounjaro, a once-weekly injection, registered for both type 2 diabetes and chronic weight management, and more recently approved for moderate-to-severe obstructive sleep apnoea in adults with obesity. Like semaglutide, it is a Schedule 4 (prescription-only) medicine.

How it works

Tirzepatide mimics two natural hormones: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). By activating both systems, it helps the pancreas release insulin in response to food, reduces glucose production, slows stomach emptying and acts on brain appetite centres to reduce hunger. The dual mechanism distinguishes it from single-pathway GLP-1 medicines like Semaglutide. It is given as a once-weekly injection, stepped up gradually to improve tolerability.

What the evidence says

Tirzepatide for weight management was studied in the SURMOUNT programme. Across SURMOUNT-1 to -4, body-weight reductions of roughly 13–23% were reported across doses in adults with obesity, with or without type 2 diabetes. In the head-to-head SURMOUNT-5 trial against semaglutide (72 weeks), tirzepatide produced a greater average reduction — about 22–23% versus around 15%. This is robust, replicated human evidence. As with semaglutide, results were achieved alongside diet and activity support, and weight tends to be regained after stopping. Head-to-head superiority does not by itself establish it is the right choice for any individual.

Legal & regulatory status in Australia

Tirzepatide is a TGA-registered prescription medicine (Schedule 4), sold as Mounjaro. It received TGA approval for chronic weight management in September 2024, in addition to its diabetes indication. Like others in the class, supply has been subject to shortages. The TGA has flagged compounded GIP/GLP-1 products as a concern and has issued alerts about counterfeit products.

Risks & considerations

The most common side effects are gastrointestinal — nausea, diarrhoea, vomiting, constipation — typically most pronounced early and during dose increases. More serious potential issues include pancreatitis and gallbladder problems, and low blood glucose with certain diabetes medicines. As a class, these carry a thyroid C-cell tumour warning based on animal data, so a personal or family history of medullary thyroid carcinoma or MEN2 is a contraindication. It is not recommended in pregnancy and may affect absorption of other oral medicines.

What to ask a doctor

• Is tirzepatide suitable for me given my medical history and other medications?
• How does it compare with other options for my situation?
• What side effects should I expect, and how are they managed?
• What monitoring and review schedule would I need?
• How do shortages affect starting and continuing treatment, and what happens if I stop?

FAQ

Q: Is tirzepatide approved in Australia? A: Yes. It is TGA-registered and prescription-only (S4) as Mounjaro, for type 2 diabetes and chronic weight management. Q: How is it different from semaglutide? A: Tirzepatide acts on two hormone pathways (GIP and GLP-1) rather than one. In the SURMOUNT-5 head-to-head trial it produced greater average weight loss, but the right choice depends on the individual. Q: Are compounded versions safe? A: The TGA has raised concerns about compounded GIP/GLP-1 products; they are not TGA-evaluated or held to the same standards as registered medicines.