Detailed Explanation
Tirzepatide is a 39-amino-acid peptide that acts as a dual agonist at both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors — the first 'twincretin' drug. It is marketed by Eli Lilly as Mounjaro (for type 2 diabetes) and Zepbound (for obesity). The peptide is based on the GIP sequence with modifications that confer GLP-1 receptor activity, acylated with a C20 fatty diacid for albumin binding and once-weekly dosing.
In the SURMOUNT-1 obesity trial, tirzepatide 15 mg achieved an average weight loss of 22.5% over 72 weeks — the largest weight reduction seen with any anti-obesity drug and approaching results previously achievable only with bariatric surgery. In diabetes (SURPASS trials), it demonstrated superior HbA1c reduction compared to semaglutide 1 mg. The dual mechanism is believed to provide complementary metabolic benefits: GLP-1 agonism provides appetite suppression and glucose control, while GIP agonism may improve fat metabolism and enhance the incretin response.
Tirzepatide represents a paradigm shift in peptide drug design — rather than targeting a single receptor, it was engineered to activate two related receptors simultaneously, exploiting the fact that GIP and GLP-1 have complementary physiological effects on metabolism. Next-generation multi-receptor agonists targeting GLP-1/GIP/glucagon (triple agonists like retatrutide) are in clinical development, building on tirzepatide's dual-agonist approach.
Key Facts
- Brand names: Mounjaro (diabetes), Zepbound (obesity)
- First dual GIP/GLP-1 receptor agonist — 'twincretin'
- 39 amino acids, based on GIP sequence with GLP-1 cross-reactivity
- SURMOUNT-1: 22.5% weight loss at 15 mg dose
- Acylated with C20 fatty diacid for weekly dosing
- Manufactured by Eli Lilly
- Outperformed semaglutide 1 mg on HbA1c reduction in SURPASS trials
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