Tirzepatide
Summary
Tirzepatide is a dual GIP/GLP-1 receptor agonist peptide with the strongest weight-loss evidence in its class: the 72-week SURMOUNT-1 trial showed ~15-21% mean weight reduction. It is FDA-approved for chronic weight management (Zepbound) and for type 2 diabetes (Mounjaro).
Mechanism
Tirzepatide is a 39-amino-acid synthetic peptide that acts as a dual agonist at the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. Receptor activation slows gastric emptying, enhances glucose-dependent insulin secretion, suppresses glucagon, and acts on appetite centers in the brain to reduce hunger and food intake. The GIP component is the differentiating feature versus GLP-1-only agonists and may contribute to its larger weight-loss effect.
Reported effects
Ratings are relative to peers in the same category, not absolute claims.
Studied dosing — research context
In SURMOUNT-1, adults with obesity received 5, 10, or 15 mg subcutaneously once weekly for 72 weeks, including a 20-week dose-escalation period. The 10 and 15 mg doses produced ~19.5% and ~20.9% mean weight loss. FDA-approved (Zepbound) for chronic weight management in adults with obesity or overweight with a weight-related condition. This describes research protocols, not guidance.
Research context only. This is not a recommendation.
Safety
The most common adverse events are gastrointestinal — nausea, diarrhea, vomiting, and constipation — usually mild to moderate and concentrated during dose escalation. It carries a boxed warning for thyroid C-cell tumors observed in rodents (human relevance unknown) and is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2. Pancreatitis and gallbladder events have been reported; it is not recommended in pregnancy.
Limitations
Most trial participants were adults with obesity; data beyond two years are still accumulating. Weight regain is common after discontinuation, as with the drug class generally. Head-to-head data against other agents for hard outcomes are limited.