Semaglutide vs Tirzepatide: how Australia's GLP-1 weight medicines compare

Semaglutide and tirzepatide are the two big names in medical weight management — and unlike most compounds in this space, both are TGA-registered. Here's the honest comparison.

The key difference: one pathway vs two

Semaglutide (Ozempic, Wegovy) is a GLP-1 receptor agonist — it mimics one gut hormone. Tirzepatide (Mounjaro) is a dual GIP/GLP-1 agonist — it acts on two. Both slow stomach emptying, improve insulin response and reduce appetite via the brain. The dual mechanism is what sets tirzepatide apart on paper.

What the trials showed

Semaglutide's STEP programme showed average weight loss around 15% over 68 weeks. Tirzepatide's SURMOUNT programme showed roughly 13–23%. In the head-to-head SURMOUNT-5 trial, tirzepatide produced a greater average reduction (about 22–23% vs ~15%). That's a real difference — but "greater average" doesn't mean "right for everyone."

Why the "best" one depends on the person

Choice depends on medical history, other conditions, tolerance of side effects (both commonly cause nausea early), supply, cost and PBS eligibility. Both tend to see weight regained after stopping, and both work best alongside diet and activity support, not instead of it.

Both are prescription medicines — and that matters

These are TGA-registered Schedule 4 medicines. That puts them in a different category to the compounded peptides elsewhere on this site. The TGA has specifically warned about compounded "semaglutide" and GLP-1 products and about counterfeits — registered product through a registered prescriber is the safe path.

The bottom line

Tirzepatide edged semaglutide on average weight loss head-to-head, but the right medicine is an individual clinical decision. Read the full explainers on semaglutide and tirzepatide, then talk to an AHPRA-registered doctor.