The short version
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It activates two gut hormone pathways simultaneously. Clinical trials show 15–22% body weight reduction at maximum tolerated doses over 72 weeks.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. It activates one pathway. Clinical trials show 12–16% body weight reduction at maximum dose over 68 weeks.
Tirzepatide delivers larger average weight reduction, but at a higher cost and with different tolerability nuances. Both are effective; the choice depends on individual factors.
Side-by-side comparison
Why dual mechanism matters
Tirzepatide's GIP-receptor activation adds something semaglutide doesn't have: GIP signalling modulates fat metabolism and may enhance lipolysis (fat breakdown) independent of the satiety pathway. This may contribute to the larger weight loss in head-to-head trials.
The SURMOUNT-5 trial (2025) directly compared tirzepatide and semaglutide head-to-head in patients without diabetes. At 72 weeks, tirzepatide groups lost an average 5.4 to 7.5 percentage points more weight than semaglutide groups. This is a clinically meaningful difference.
How our doctors choose
When tirzepatide makes more sense
- Larger weight loss target (BMI >35, or co-existing metabolic syndrome)
- Type 2 diabetes co-management (HbA1c reduction is meaningfully larger with tirzepatide)
- Patient has tried semaglutide and plateaued or had insufficient response
When semaglutide makes more sense
- Cost sensitivity (semaglutide is typically lower-cost than tirzepatide in Singapore)
- Longer safety track record preferred (semaglutide has been in clinical use longer)
- Patient prefers a single-mechanism agent (some prefer dose-titration on a more familiar pathway)
Switching between them
Switching is medically reasonable in two scenarios:
- Plateau: If weight loss stalls on maximum semaglutide dose, switching to tirzepatide can sometimes restart progress
- Tolerability: Patients who can't tolerate one occasionally tolerate the other better, despite similar mechanism
Switching requires medical supervision — dose conversion is not 1:1, and there's a re-titration period.
Honest considerations beyond weight loss
"Rebound" risk
Both medications, when stopped, are typically followed by weight regain. The STEP-1 follow-up trial showed average regain of 2/3 of lost weight within 12 months of stopping semaglutide. Similar patterns are emerging for tirzepatide. This is not a failure of the medication — it's that the medication treats the symptom (appetite, satiety) while the underlying biology continues.
Long-term success requires either (a) sustained medication use, or (b) substantial behavioural / lifestyle change during the medication phase that endures after stopping. Both are clinically reasonable strategies.
Muscle mass preservation
Significant weight loss from any source carries some muscle-mass loss alongside fat loss. Resistance training and adequate protein intake during the active loss phase help preserve muscle. Without these, total lean mass loss can be 20-25% of total weight loss — not ideal for long-term metabolic health.
Cosmetic considerations
Both medications can produce the so-called "Ozempic face" (or "Mounjaro face") — perceived facial gauntness from fat loss in cheeks and temples. This is a consequence of rapid weight loss, not the medication specifically. Aesthetic management strategies (bio-remodellers, collagen-stimulators, non-surgical lifting) are commonly used concurrently or post-loss.
What to do next
The right medication depends on your specific medical profile, weight loss target, and economic considerations. A consultation begins with full medical history and goal-setting, then your doctor will recommend the appropriate agent.