Underground Biohacking
Metabolic

Retatrutide

Chris Hallewell, founder of Underground Biohacking

By , Founder, Underground Biohacking

Last reviewed

Investigational / clinical trial

Retatrutide is an experimental drug. It is not approved anywhere in the world. Eli Lilly is still testing it, and the published human results come from phase 1 and phase 2 trials. In those trials it cut body weight, blood sugar and liver fat in adults with obesity or type 2 diabetes. Phase 3 trials are running now. Nobody knows yet how safe it is over years, and there is no lawful way to get it.

What is Retatrutide?

Retatrutide is a lab made peptide, which means a short chain of amino acids. Eli Lilly designed it and gave it the code name LY3437943. It is a triple agonist. That means one molecule switches on three different receptors at once. Those three targets are the GLP-1 receptor, the GIP receptor and the glucagon receptor. GLP-1 and GIP are gut hormones. They help tell your brain you have eaten, and they help the pancreas release insulin. Glucagon is a third hormone. It signals the liver and shapes how the body handles stored fuel. The third target is what sets retatrutide apart. Most weight drugs on the market hit fewer targets. Semaglutide, approved and sold as Ozempic and Wegovy, works through GLP-1 alone. Tirzepatide adds GIP. Retatrutide adds glucagon on top of both. Researchers built it that way hoping the extra target would add to the effect on weight. In the published trials it was given as an injection under the skin, once a week.

What is Retatrutide prescribed for?

  • In adults with obesity, weekly injections cut body weight over 48 weeks in a phase 2 trial.[2]Human study
  • In people with type 2 diabetes, a phase 2 trial found better blood sugar control and lower body weight.[3]Human study
  • In people with fatty liver disease, liver fat fell, and the fall tracked with weight and belly fat loss.[4]Human study
  • In trial participants, albumin in the urine (a kidney strain marker) fell, and filtration improved in those with obesity.[5]Human study
  • Pooled across randomised trials in adults with obesity, body weight and metabolic markers both improved.[7]Human study
  • In obese mice and hamsters fed a fatty diet, it produced several metabolic benefits.[9]Animal or lab study only
  • In diabetic db/db mice, it cut weight and improved kidney function more than two comparison drugs.[10]Animal or lab study only

How does Retatrutide work?

Retatrutide adds a third target. It activates the GLP-1 and GIP receptors, then the glucagon receptor as well. Glucagon is the hormone that normally raises blood sugar, so this sounds backwards. The point is its other jobs. Glucagon pushes your liver to burn stored fat and raises the energy you burn at rest. The GLP-1 arm holds the blood sugar rise in check, so the two balance out. That balance is the open question. Researchers still don't agree on the best ratio of glucagon signal to GLP-1 signal. That ratio is what makes one of these drugs behave differently from another.

Educational reference only. Talk to a licensed clinician for any decisions on Retatrutide.

What are the side effects of Retatrutide?

EffectHow seriousWhat to watch
Gut side effects and hypersensitivity (allergic type) reactions happened more often than with placebo.[6]Common, reported as non-severeSickness, vomiting, loose stools, rash or swelling
Heart rate rose. The rise was larger at higher amounts, peaked around week 24, then fell back.[2]Dose related, then decliningResting pulse
Across trials it caused more side effects overall than drugs that act on fewer receptors.[8]Higher than comparator drugsHow well you tolerate it, above all gut symptoms
In the phase 2 diabetes trial, nobody had severe low blood sugar and nobody died.[3]None reported in that trialShaking, sweating or confusion, if other diabetes drugs are also used
The earliest human trial called the safety profile acceptable, but it was small and short.[1]Unknown beyond trial lengthNone

Is Retatrutide legal in 2026?

Checked on 6 August 2026. Retatrutide is investigational. It holds no marketing approval from the FDA or from any other regulator. A search of the FDA drug approval database returns no record for it at all. It is also absent from the FDA list of bulk drug substances that may present significant safety risks. It was never nominated for pharmacy compounding. That list records compounding nominations. It is not a licence, and being absent from it does not make a substance lawful to compound, prescribe or sell. The only lawful way to receive retatrutide is as a participant in a registered clinical trial. Phase 3 trials are still running, and their results are not published yet.

Status checked against the primary source.

Educational reference only. Talk to a licensed clinician for any decisions on Retatrutide.

If you are considering Retatrutide

This page does not provide dosing, cycling, stacking, or sourcing guidance for Retatrutide. The protocol conversation belongs with a licensed clinician who can review your bloodwork, history, and goals.

Where to buy Retatrutide

Running Retatrutide in your next protocol cycle?

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Frequently Asked Questions

Is retatrutide approved by the FDA?
No. Retatrutide has no approval from the FDA or any other regulator, and it is not approved in any country. It sits in phase 3 testing, which is the last stage before a company can apply for approval. Nothing about that stage makes it available. The FDA drug approval database holds no record for it. Any product sold to the public under this name is outside the regulated system entirely.
What did the trials actually show?
Two phase 2 trials carry most of the evidence. In adults with obesity, 48 weeks of treatment produced substantial weight loss. In adults with type 2 diabetes, blood sugar control improved and weight fell. A substudy in people with fatty liver disease showed liver fat dropping alongside weight and belly fat. A kidney analysis found a urine marker of kidney strain falling. All of this is phase 2 work, not phase 3.
How is it different from semaglutide and tirzepatide?
It hits one more target. Semaglutide, approved as Ozempic and Wegovy, acts on the GLP-1 receptor. Tirzepatide acts on GLP-1 and GIP. Retatrutide acts on GLP-1, GIP and glucagon. In a pooled comparison across trials, it produced more weight loss than the GLP-1 only drugs. It also came with a higher rate of side effects. The two approved drugs have far longer safety records behind them.
What are the known risks?
Gut problems are the most common issue reported, and allergic type reactions came up more often than with placebo. Heart rate went up during treatment, more so at higher amounts, then settled after about six months. Pooled trial data shows a higher overall side effect rate than for drugs with fewer targets. In the phase 2 diabetes trial no one had severe low blood sugar and no one died.
Is it safe over the long term?
Nobody knows. The published human trials ran for months, not years, and they enrolled a few hundred people each. That is enough to spot common side effects and far too little to spot rare or slow ones. Phase 3 trials exist partly to answer this question, and their results are not out. Anyone claiming a long term safety record for retatrutide is describing evidence that has not been published.
What should I ask a doctor about it?
Ask what your actual goal is, then what approved treatments already meet it. Approved options for weight and blood sugar have published long term data and a licensed supply chain, and retatrutide has neither. If the trial results interest you, ask whether you might qualify for a registered clinical trial near you. Ask what monitoring any approved treatment would need. That is a conversation your doctor can act on.

References

  1. 1.Urva S, et al. (2022). LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. PMID: 36354040. DOI: 10.1016/S0140-6736(22)02033-5.
  2. 2.Jastreboff AM, et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. The New England journal of medicine. PMID: 37366315. DOI: 10.1056/NEJMoa2301972.
  3. 3.Rosenstock J, et al. (2023). 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. Lancet. PMID: 37385280. DOI: 10.1016/S0140-6736(23)01053-X.
  4. 4.Sanyal AJ, et al. (2024). Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature medicine. PMID: 38858523. DOI: 10.1038/s41591-024-03018-2.
  5. 5.Heerspink HJL, et al. (2025). The Effect of Retatrutide on Kidney Parameters in Participants With Type 2 Diabetes Mellitus and/or Obesity. Kidney international reports. PMID: 40630318. DOI: 10.1016/j.ekir.2025.03.049.
  6. 6.Pasqualotto E, et al. (2024). Effects of once-weekly subcutaneous retatrutide on weight and metabolic markers: A systematic review and meta-analysis of randomized controlled trials. Metabolism open. PMID: 39318607. DOI: 10.1016/j.metop.2024.100321.
  7. 7.Abdrabou Abouelmagd A, et al. (2025). Efficacy and safety of retatrutide, a novel GLP-1, GIP, and glucagon receptor agonist for obesity treatment: a systematic review and meta-analysis of randomized controlled trials. Proceedings (Baylor University. Medical Center). PMID: 40291085. DOI: 10.1080/08998280.2025.2456441.
  8. 8.Sinha B, Ghosal S. (2025). Efficacy and Safety of GLP-1 Receptor Agonists, Dual Agonists, and Retatrutide for Weight Loss in Adults With Overweight or Obesity: A Bayesian NMA. Obesity (Silver Spring, Md.). PMID: 40685589. DOI: 10.1002/oby.24360.
  9. 9.Briand F, et al. (2026). Retatrutide Shows Multiple Metabolic Benefits in Diet-Induced Obese MASH Mouse and Hamster Models. Obesity (Silver Spring, Md.). PMID: 41741376. DOI: 10.1002/oby.70155.
  10. 10.Ma J, et al. (2024). Comparison of the effects of Liraglutide, Tirzepatide, and Retatrutide on diabetic kidney disease in db/db mice. Endocrine. PMID: 39212900. DOI: 10.1007/s12020-024-03998-8.

One more time, because it matters

This page exists to identify Retatrutide and explain what the research describes. Underground Biohacking does not advise on dosage, cycling, stacking, or where to source prescription compounds. If Retatrutide is part of your plan, that conversation belongs with a clinician who can review your labs, history, and goals. Not with a website.