Overview
Ozempic (semaglutide) and Mounjaro (tirzepatide) are both prescription medications in the incretin-based therapy class — they work by activating receptors involved in hormonal regulation of insulin secretion, glucagon suppression, and appetite signalling. However, they differ meaningfully in their pharmacological mechanism.
| Factor | Ozempic (Semaglutide) | Mounjaro (Tirzepatide) |
|---|---|---|
| Active ingredient | Semaglutide | Tirzepatide |
| Receptor mechanism | GLP-1 receptor agonist (single) | Dual GIP + GLP-1 receptor agonist |
| Dosing | Once weekly injection | Once weekly injection |
| ARTG-registered | Yes | Yes |
| PBS listing | Yes (for T2D indication) | No (private access) |
| Schedule | S4 — Prescription Only | S4 — Prescription Only |
| Manufacturer | Novo Nordisk | Eli Lilly |
The Mechanism Difference
The core pharmacological difference between the two medications is the number and type of receptors they activate:
Ozempic (Semaglutide) — GLP-1 Receptor Agonist
Semaglutide binds selectively to and activates GLP-1 (glucagon-like peptide-1) receptors. GLP-1 is a naturally occurring gut hormone with roles in:
- Glucose-dependent insulin secretion (stimulating insulin release in response to elevated blood glucose)
- Glucagon suppression (reducing glucose production from the liver)
- Gastric emptying (slowing the rate at which food leaves the stomach)
- Appetite signalling via GLP-1 receptors in the hypothalamus and brainstem
Mounjaro (Tirzepatide) — Dual GIP/GLP-1 Receptor Agonist
Tirzepatide is an engineered molecule that activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors simultaneously. In addition to the GLP-1 mechanisms described above, GIP receptor activation is associated with:
- Glucose-dependent insulin secretion via the GIP pathway (a separate but overlapping mechanism)
- Potential influences on adipose (fat) tissue metabolism
- Possible synergistic effects when combined with GLP-1 receptor activation
The dual agonism of tirzepatide represents a distinct pharmacological advance over single-agent GLP-1 medications and is the subject of ongoing research into its clinical implications.
What the Clinical Research Shows
Both medications have been evaluated in large-scale randomised controlled trials. The trials used different study populations, doses, and timeframes — meaning the data are not directly comparable head-to-head.
STEP Programme (Semaglutide)
The STEP trial programme evaluated semaglutide specifically at the Wegovy dose (2.4mg weekly — a different product to Ozempic). STEP 1 (Wilding et al., NEJM, 2021) reported an average body weight change of approximately −14.9% over 68 weeks in the semaglutide group vs −2.4% in the placebo group.
SURMOUNT Programme (Tirzepatide)
The SURMOUNT programme evaluated tirzepatide at 5mg, 10mg, and 15mg weekly doses. SURMOUNT-1 (Jastreboff et al., NEJM, 2022) reported an average body weight change of approximately −20.9% (15mg group) vs −3.1% (placebo) over 72 weeks.
Which is Right for You?
This is a clinical decision — not a consumer choice. The appropriate medication for an individual patient depends on factors that only a prescriber can properly assess: medical history, comorbidities, current medications and potential interactions, cost and access considerations, personal preferences regarding administration, and contraindications specific to each medication.
No single medication is universally superior. Your prescriber is best placed to recommend — or determine — what is appropriate and safe for your circumstances.