What is tirzepatide?
Tirzepatide (Mounjaro) is a dual agonist from Eli Lilly that activates both the GLP-1 and GIP receptors. As a medicine it is approved in the EU for type 2 diabetes and weight management and is prescribed by a doctor.
Key facts
- Mechanism: GLP-1 and GIP receptor agonist
- Half-life: about 5 days
- Doses studied: 5, 10 and 15 mg once weekly
- Approved medicine: Mounjaro
How does dual agonism work?
- GLP-1: reduces appetite, slows gastric emptying and improves insulin release.
- GIP: improves insulin sensitivity and influences fat-cell metabolism.
The combination is thought to explain why tirzepatide produces greater weight loss than substances that act on GLP-1 alone.
Doses and results in the trials
In SURMOUNT-1 (2,539 participants with obesity, 72 weeks), everyone started on 2.5 mg per week and the dose was increased by 2.5 mg every four weeks until the target dose was reached. Results by target dose:
| Target dose | Average weight loss |
|---|---|
| 5 mg | 15.0% |
| 10 mg | 19.5% |
| 15 mg | 20.9% |
| Placebo | 3.1% |
These figures are research data, not recommendations.
Side effects in the trials
As with other substances in the class, gastrointestinal side effects were most common – nausea, diarrhoea, constipation and vomiting – mainly during dose escalation and more often at higher doses. Most were mild to moderate.
Tirzepatide vs semaglutide
| Property | Tirzepatide | Semaglutide |
|---|---|---|
| Mechanism | GLP-1 + GIP | GLP-1 only |
| Weight loss (trials) | ~21% (72 wk) | ~15% (68 wk) |
| Head-to-head | SURMOUNT-5 (2025): tirzepatide produced greater weight loss than semaglutide after 72 weeks | |
The next step in this line of research is the triple agonist retatrutide, which also activates the glucagon receptor. See our retatrutide research guide or retatrutide prices and stock.
This is a summary of published research and is not medical advice. Research peptides are not intended for humans or animals.