Tirzepatide
The leading GLP-1/GIP dual agonist right now. FDA-approved and outperforming semaglutide in head-to-head weight trials.
What is tirzepatide?
Tirzepatide is a once-weekly, FDA-approved peptide that hits two gut-hormone receptors at once, GIP and GLP-1, which is why it gets called a "twincretin." It is sold as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management. In head-to-head weight trials it has outperformed semaglutide, making it the strongest approved option in this category right now.
How tirzepatide works
Semaglutide activates one incretin receptor. Tirzepatide activates two. It agonizes both the GLP-1 receptor and the GIP receptor, and that combination drives complementary effects across the pancreas, fat tissue, and the appetite centers of the brain: more glucose-dependent insulin release, better lipid handling, slowed gastric emptying, and stronger appetite suppression. The prevailing view is that adding GIP signaling on top of GLP-1 is what pushes its weight-loss numbers past the GLP-1-only drugs.
What the research shows
In the SURMOUNT-1 obesity trial, adults without diabetes on the 15 mg dose lost an average of 20.9% of body weight over 72 weeks, versus 3.1% on placebo. The 10 mg and 5 mg doses landed at 19.5% and 15.0%. More than half of the 15 mg group (56.7%) lost at least 20% of their body weight, a threshold once associated with bariatric surgery. Separately, the SURPASS program established its diabetes credentials with large A1c reductions. This is deep, randomized, human-trial evidence.
Dosage and how it is used
Tirzepatide starts at 2.5 mg once weekly, a tolerability dose rather than a therapeutic one, and steps up by 2.5 mg no sooner than every four weeks toward a maximum of 15 mg, an escalation that spans roughly 20 weeks. As with semaglutide, the slow ramp exists to keep the gastrointestinal side effects manageable, and pushing the dose faster does not improve the outcome.
→ How to reconstitute tirzepatide: calculator, units to draw & storage
Side effects and safety
The side effects mirror the GLP-1 class and are mostly gastrointestinal. In SURMOUNT-1, nausea affected about 31% of the 15 mg group versus 11.7% on placebo, and diarrhea about 22%. They cluster around dose increases and usually ease within a week or two. Discontinuation for side effects was about 6.3%, comparable to semaglutide. Tirzepatide carries the same thyroid C-cell tumor boxed warning as other incretin drugs and is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2.
- Research depth: extensive. Human clinical trials: yes, large and randomized.
- GI side effects are common but usually transient and tied to dose increases.
- Prescription medicine in the US. Verify current legal and regulatory status independently.
Frequently asked questions
How much weight can you lose on tirzepatide?
In SURMOUNT-1, adults with obesity on the 15 mg dose lost an average of 20.9% of body weight over 72 weeks, versus 3.1% on placebo. The 5 mg dose still produced about 15%. Individual results vary, and weight tends to return if treatment stops without lasting lifestyle change.
How is tirzepatide different from semaglutide?
Semaglutide targets the GLP-1 receptor alone. Tirzepatide targets GLP-1 and GIP together, and that dual action is why it has produced larger average weight loss in trials. Both are once-weekly injections with similar side-effect profiles.
What is the tirzepatide dosing schedule?
It starts at 2.5 mg once weekly and increases by 2.5 mg no more often than every four weeks, up to a maximum of 15 mg. The full ramp takes about 20 weeks. The 2.5 mg start is for tolerability, not effect.
Is tirzepatide FDA-approved?
Yes. It is approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management. It is the same molecule under both brand names.
References
Track Tirzepatide in Peptide AI
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