Tirzepatide (Mounjaro) and semaglutide (Ozempic, Wegovy, Rybelsus) are the two most-asked-about weight-management medicines in Australia in 2026. Both are GLP-1-class drugs, both are prescribed by Australian doctors, and both are paid privately for weight loss — but they're not interchangeable. Here's the honest comparison.
Mechanism: Semaglutide is a single GLP-1 receptor agonist. Tirzepatide is a dual GIP and GLP-1 receptor agonist — it acts on two metabolic pathways instead of one. In practice that means tirzepatide tends to produce more weight loss at comparable doses, with a similar side-effect profile.
Head-to-head efficacy: the SURMOUNT and STEP trials are not direct head-to-head, but cross-trial comparisons consistently show tirzepatide 15 mg producing average weight loss in the 20–22% range over ~72 weeks versus semaglutide 2.4 mg in the 14–17% range. For type 2 diabetes glycaemic control, tirzepatide also tends to produce greater HbA1c reductions. Individual response varies widely — some people lose more on semaglutide than the average tirzepatide patient.
Side effects: Both cause GI side effects in the first 4–8 weeks of titration — nausea, reflux, constipation, occasionally vomiting. The pattern is similar; severity is roughly comparable. Both carry a boxed warning for personal/family history of medullary thyroid carcinoma or MEN2 and should not be used in pregnancy or breastfeeding. Pancreatitis risk is small but present with both.
Cost in Australia (2026): Mounjaro (tirzepatide) runs roughly AUD $400–$650/month private script depending on dose. Wegovy (semaglutide for weight loss) is roughly AUD $460–$520/month. Ozempic (semaglutide for diabetes, used off-label for weight loss) is roughly AUD $130/month on the PBS for eligible diabetes patients, or ~$300/month private — but availability has been heavily constrained and TGA has explicitly asked prescribers to prioritise diabetic patients. Compounded tirzepatide or semaglutide via SAS-B can sit lower but is a per-case clinical decision, not a default cheaper option.
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PBS status (2026): Mounjaro is PBS-listed for type 2 diabetes under specific criteria, not for weight management. Ozempic is PBS-listed for type 2 diabetes only. Wegovy is not PBS-subsidised. For weight management without diabetes, all three are private prescriptions.
How to get either prescribed in Australia: Both require an AHPRA-registered Australian doctor's prescription after a clinical assessment confirming you meet criteria (typically BMI ≥30, or ≥27 with weight-related comorbidities, or type 2 diabetes). For branded Mounjaro / Wegovy / Ozempic the doctor issues a standard private prescription dispensed at any Australian pharmacy. Compounded preparations require the SAS-B pathway through a TGA-licensed compounding pharmacy.
So which one? Talk to your prescriber — that's not a cop-out, it's the honest answer. Practical considerations: tirzepatide tends to produce more weight loss but is more expensive; semaglutide has a longer clinical track record (it's been in widespread use since 2017); Ozempic supply for non-diabetic weight loss is ethically and practically constrained; Wegovy is the on-label semaglutide weight-loss product. If GI side effects are a deal-breaker for you, slow titration on either drug helps more than switching molecules.
Avoid: any "tirzepatide" or "semaglutide" sold online without an Australian prescription. The unregulated supply chain carries no guarantee of identity, potency, or sterility, and importing it is an offence under the Customs Act regardless of how the vendor labels the vial.
If you'd like to be assessed for either, start with our 5-minute intake. An AHPRA-registered Australian doctor will review your history, BMI, comorbidities, and preferences and recommend the right molecule and pathway for you.