Dr. Pep

Peptides · GIP/GLP-1/glucagon triple receptor agonist

Retatrutide: what the studies show

Every line below comes from a study, label or regulator record, checked by two models, with the source linked. Information, not medical advice. For adults 18+.

What it is

  • Retatrutide (also called LY3437943) is an experimental once-weekly injection that activates three receptors: GIP, GLP-1 and glucagon. Eli Lilly is testing it for obesity, type 2 diabetes and other conditions.[1][2]
  • It is not an approved drug. FDA says retatrutide is not a component of any FDA-approved drug and has not been found safe and effective for any condition (page updated 2026).[3]

Bottom line

  • Retatrutide has produced very large weight loss in company-run phase 2 and phase 3 trials, but it is still investigational, long-term safety is unknown, and products sold online as retatrutide are unapproved and unverified.[4][1][3]

What the human studies found

  • Phase 2 obesity trial (double-blind RCT, 338 adults, weekly injections, Lilly-funded): at 48 weeks body weight fell 8.7% on 1 mg, 17.1% on pooled 4 mg, 22.8% on pooled 8 mg and 24.2% on 12 mg, versus 2.1% on placebo.[1]
  • Phase 3 TRIUMPH-1 (double-blind RCT, 2,339 adults with obesity and no diabetes, 80 weeks): weight fell 17.6% on 4 mg, 23.7% on 9 mg and 25.0% on 12 mg, versus 3.9% on placebo. In the sleep apnoea subgroup, events per hour fell by 22.9 to 34.3 on retatrutide versus 9.9 on placebo; knee osteoarthritis pain scores improved more than on placebo.[4]
  • Phase 3 TRIUMPH-2 (double-blind RCT, 1,152 adults with obesity and type 2 diabetes, 80 weeks): weight fell 11.9% on 4 mg, 16.8% on 9 mg and 18.8% on 12 mg, versus 5.1% on placebo.[2]
  • Phase 2 trial in type 2 diabetes (RCT, 281 adults, 24 weeks): HbA1c fell by up to 2.02 points on retatrutide 12 mg versus 0.01 on placebo and 1.41 on dulaglutide 1.5 mg. Weight at 36 weeks fell up to 16.94% versus 3.00% on placebo.[5]
  • In a liver sub-study of the phase 2 obesity trial (RCT, 98 adults with fatty liver), liver fat fell 81-82% at 24 weeks on 8 and 12 mg versus a 0.3% rise on placebo.[6]

Known risks and side effects

  • In the phase 2 obesity trial, the most common side effects were stomach-related and dose-related, and heart rate rose in a dose-dependent way, peaking at 24 weeks and then declining.[1]
  • In TRIUMPH-2, diarrhoea affected 27-34% on retatrutide versus 13% on placebo, nausea 14-28% versus 8%, dysaesthesia (odd skin sensations) 4-7% versus 1%, and low blood pressure 1-6% versus under 1%. 12% on 9 mg and 8% on 12 mg stopped because of side effects or death, versus 5% on placebo.[2]
  • Case reports of online-sourced products labelled retatrutide: a man with type 1 diabetes developed severe vomiting, high blood sugar, ketones and kidney injury soon after self-injecting one. A woman in her mid-20s had five days of refractory nausea after four weekly escalating injections from an unverified product given in a wellness setting; it settled within a week of stopping. In both, what the vials contained was not confirmed.[7][8]

Legal status

  • As of the FDA page updated in 2026, retatrutide cannot be used in compounding under federal law and is not part of any approved drug. FDA says it has warned telehealth companies, API distributors and outsourcing facilities over retatrutide.[3]
  • FDA warning letters to sellers of 'research use only' or compounded retatrutide include Swisschems and Xcel Research (2024-12-10), Amazing Meds and GLP-1 Solution (2025-09-09), GenoGenix (2026-01-20), Gram Peptides and Prime Sciences (2026-03-31) and Peptide Partners (2026-08-24).[9][10][11][12][13][14][15][16]

Sources

  1. [1] Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial.
  2. [2] Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial.
  3. [3] FDA: FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (updated 2026)
  4. [4] Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity.
  5. [5] Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA.
  6. [6] Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial.
  7. [7] Online-Sourced Retatrutide Complicating Impending Diabetic Ketoacidosis in a Patient With Type 1 Diabetes and Concurrent Shigella Gastroenteritis.
  8. [8] Emerging risks of health optimisation: refractory nausea associated with peptide injections reported to contain retatrutide.
  9. [9] FDA: Warning Letter, Swisschems (2024-12-10), research-use-only retatrutide and semaglutide
  10. [10] FDA: Warning Letter, Xcel Research LLC (2024-12-10), retatrutide, semaglutide, cagrilintide, survodutide, mazdutide, sermorelin
  11. [11] FDA: Warning Letter, Amazing Meds (2025-09-09), retatrutide and semaglutide
  12. [12] FDA: Warning Letter, GLP-1 Solution (2025-09-09), compounded retatrutide, semaglutide, tirzepatide
  13. [13] FDA: Warning Letter, GenoGenix LLC (2026-01-20), compounded NAD+, thymosin beta-4, semaglutide, tirzepatide, retatrutide
  14. [14] FDA: Warning Letter, Gram Peptides (2026-03-31), research-use-only retatrutide and tirzepatide
  15. [15] FDA: Warning Letter, Prime Sciences (2026-03-31), retatrutide, cagrilintide, mazdutide, semaglutide, tirzepatide
  16. [16] FDA: Warning Letter, Peptide Partners LLC (2026-08-24), research-use-only semaglutide, tirzepatide, retatrutide, tesamorelin, PT-141