What it is
Tirzepatide is a once-weekly injectable that activates two gut-hormone receptors at the same time: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Acting on both is what sets it apart from earlier single-target drugs like semaglutide. It is the only compound in this library with full regulatory approval and a large body of phase 3 evidence behind it.
It is approved at the same doses, 5mg, 10mg and 15mg, for both type 2 diabetes and chronic weight management, taken alongside diet and activity changes.
How it works
GLP-1 and GIP are hormones your gut releases after eating. They prompt the pancreas to release insulin when blood sugar is high, slow how fast the stomach empties, and act on appetite centres in the brain. By stimulating both receptors, tirzepatide reduces appetite and food intake while improving how the body handles glucose.
What the evidence shows
The phase 3 SURMOUNT programme is the headline evidence. In SURMOUNT-1, the largest trial in adults with obesity, results were dose-dependent and substantial.
In that trial, participants on tirzepatide lost an average of 35 to 52 pounds over 72 weeks, against just 2.4% on placebo. Around 96% of those on the higher doses achieved at least 5% body weight reduction, compared with 28% on placebo.
A later head-to-head trial, SURMOUNT-5, compared it directly against semaglutide over 72 weeks. Tirzepatide produced a 20.2% average weight reduction versus 13.7% for semaglutide, the first direct clinical comparison of the two leading drugs.
Reported side effects
Across the trials the most common adverse events were gastrointestinal: nausea, diarrhoea and constipation. These were generally mild to moderate, tended to occur during the dose-escalation period, and eased over time. The overall safety profile was described as similar to other incretin-based therapies.
Where it stands
Tirzepatide is a prescription medicine. It is the benchmark the other compounds in this library are measured against: a real approval, large randomised trials, and a defined safety profile. That does not make it right for everyone, and it carries genuine side effects, but the evidence is in a different league to the research-only compounds.