As of: November 7, 2026 · Sources: New England Journal of Medicine
Tirzepatide is an active ingredient from Eli Lilly that simultaneously activates the receptors for the gut hormones GIP and GLP-1. In the pivotal SURMOUNT-1 trial, obese adults receiving the highest dose of 15 mg lost an average of 20.9% of their body weight after 72 weeks, compared to 3.1% with placebo [1]. Tirzepatide is approved under the brand names Mounjaro® and Zepbound® for the treatment of type 2 diabetes and obesity.
How does Tirzepatide work?
Tirzepatide is a dual agonist. It binds to two receptors involved in the regulation of appetite and blood sugar:
- GLP-1 receptor: It promotes glucose-dependent insulin secretion, inhibits glucagon release, slows gastric emptying, and increases the feeling of satiety.
- GIP receptor: It also enhances glucose-dependent insulin secretion and complements the GLP-1 effect.
Unlike Semaglutide, Tirzepatide acts on two receptors instead of one. Retatrutide additionally activates the glucagon receptor.
What do the studies on Tirzepatide show?
SURMOUNT-1 registration study (2022)
SURMOUNT-1 studied 2,539 adults with obesity or overweight without diabetes over 72 weeks [1]. The mean weight change was −15.0% (5 mg), −19.5% (10 mg), and −20.9% (15 mg), compared with −3.1% with placebo. With 10 mg and 15 mg, 50% and 57% of participants, respectively, achieved a weight reduction of at least 20%, compared with 3% with placebo.
The frequently cited figure of 22.5% comes from an additional analysis of the same study, which shows what the results would have been if all participants had continued the treatment as planned. The main analysis across all participants yields 20.9%.
Direct comparison with Semaglutide: SURMOUNT-5 (2025)
In the SURMOUNT-5 trial, 751 adults with obesity without diabetes received either Tirzepatide or Semaglutide at the highest tolerated dose for 72 weeks [2]. Body weight decreased by 20.2% with Tirzepatide and by 13.7% with Semaglutide. Waist circumference decreased by 18.4 cm and 13.0 cm, respectively.
What side effects were observed?
Gastrointestinal disturbances were the most common adverse event [1][2]. They were mostly mild to moderate and occurred primarily during the dose escalation phase. In SURMOUNT-1, 4.3% to 7.1% of participants discontinued treatment due to adverse events while receiving Tirzepatide, compared to 2.6% in the placebo group [1].
How does Tirzepatide differ from Semaglutide and Retatrutide?
The most important difference lies in the number of activated receptors. The table shows the main results of the respective registration and phase 3 trials, evaluated across all participants:
| Active ingredient | Receptors | Average weight change | Study | Status |
|---|---|---|---|---|
| Semaglutide | GLP-1 | -14.9% after 68 weeks | STEP 1 [3] | approved |
| Tirzepatide | GLP-1, GIP | -20.9% after 72 weeks (15 mg) | SURMOUNT-1 [1] | approved |
| Retatrutide | GLP-1, GIP, Glucagon | -25.0% after 80 weeks (12 mg) | TRIUMPH-1 [4] | not approved yet |
The studies are not directly comparable because they differ in duration, dosage, and participants.
A detailed comparison of all three active ingredients.
Storage and shelf life of Tirzepatide
Tirzepatide is supplied as a lyophilized (freeze-dried) powder. Dry, light-protected storage at 2–8 °C is recommended. After dissolving in BAC water (bacteriostatic water), the solution should be refrigerated and used within 4 weeks.
All details are in the storage instructions.
Where can I buy Tirzepatide?
Reta24 offers Tirzepatide as a research peptide in strengths of 10 mg, 20 mg, 30 mg, and 60 mg. Each batch is tested by HPLC for a purity of at least 98.9%. Shipping is from Germany.
View all dosages and current prices of Tirzepatide.
Sources
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med 2022;387:205–216. doi:10.1056/NEJMoa2206038
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med 2025;393:26–36. doi:10.1056/NEJMoa2416394
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med 2021;384:989–1002. doi:10.1056/NEJMoa2032183
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med 2026;395:1781–1793. doi:10.1056/NEJMoa2604169
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