No one can write you a script for retatrutide today. Here is what the trials say while we wait.

The short version

Retatrutide (LY3437943) is an investigational peptide developed by Eli Lilly. It works by activating three hormone receptors at once — GLP-1, GIP, and glucagon — which is why it is called a triple agonist. Most weight-loss drugs in use today activate one or two of these pathways. The glucagon arm adds calorie-burning on top of the appetite suppression and blood-sugar control the others provide.

As of mid-2026, retatrutide cannot be prescribed. It has no approved indication in any country. Phase 3 trials are running, and two of them (TRIUMPH-1 and TRIUMPH-4) have reported topline numbers. A realistic path to a pharmacy SKU is still at minimum one to two years away.

This site reads the published trial record carefully and reports what the studies actually measured. For what the research community reports from personal experience — benefits and side effects, labeled anecdotal — see the effects page.

What retatrutide is, in one paragraph

Retatrutide is a synthetic 39-amino-acid peptide engineered on a glucagon backbone, with substitutions that let one molecule activate three distinct hormone receptors at once: GLP-1, GIP, and glucagon ^[1]. A C20 diacid fatty acid tail binds reversibly to circulating albumin and stretches the terminal half-life to roughly six days in healthy volunteers, which is what permits once-weekly subcutaneous dosing ^[2]. Eli Lilly developed it under the code LY3437943; the public-facing International Nonproprietary Name is retatrutide. It is not a brand. There is no approved product, no labeled indication, and no pharmacy SKU. As of mid-2026 the molecule remains investigational, with Phase 3 readouts arriving from the TRIUMPH program one trial at a time ^[5].

Why this site exists

Most public writing about retatrutide either summarizes a single press release or extrapolates from it. The trial record is larger than that — two Phase 2 trials, a Phase 2a hepatic-fat substudy, a first-in-human pharmacokinetics study, and an unfolding Phase 3 program with multiple population arms ^{[1][2][3][7][15]}. This site reads the trials in their published form and reports what they actually measured.

The domain name carries the word 'prescribed.' That is editorial framing, not a service offer. Retatrutide cannot be prescribed in the United States or anywhere else right now: it is not on a label, it is not on the FDA's 503A bulk drug list, and it is not eligible for 503B outsourcing-facility compounding while it remains under active development by its sponsor. Visitors searching for a path to a prescription should understand that the path does not exist yet. When it does — likely a year or more after the first NDA filing — clinicians, not editorial sites, will be the ones writing scripts.

What the trials report at a glance

The Phase 2 obesity trial published in the New England Journal of Medicine in 2023 reported a 24.2% mean body-weight reduction at week 48 in the 12 mg arm, compared with 2.1% on placebo ^[1]. The Phase 2 type-2-diabetes trial in the Lancet reported HbA1c reductions of 2.02 percentage points from a baseline of 8.3%, with up to 71% of participants on 12 mg reaching HbA1c below 5.7% ^[2]. A Phase 2a substudy in Nature Medicine reported an 86% relative reduction in liver fat by MRI-PDFF at week 48 on the 12 mg dose, with 93% of participants achieving normalization of hepatic fat fraction ^[3].

The Phase 3 program is now in motion. TRIUMPH-1, the pivotal obesity trial in 2,339 adults without diabetes, reported a mean weight loss of 28.3% at week 80 on the 12 mg arm, with 45.3% of participants achieving at least 30% body-weight reduction ^[5]. TRIUMPH-4, the obesity-with-knee-osteoarthritis trial of 445 adults, reported 28.7% mean weight loss and a roughly 75.8% relative reduction in WOMAC pain at week 68, along with a 14.0 mmHg drop in systolic blood pressure on the 12 mg arm ^[6]. The full cardiovascular outcomes trial, TRIUMPH-Outcomes, in approximately 10,000 adults with obesity and established cardiovascular disease, has not yet read out ^[15].

What is not yet known

Long-term safety beyond roughly 80 to 104 weeks of continuous exposure is unstudied. The MACE composite endpoint — cardiovascular death, non-fatal myocardial infarction, non-fatal stroke — is being measured in TRIUMPH-Outcomes and will not deliver a verdict for years ^[15]. A distinctive adverse event, cutaneous dysesthesia (an abnormal tingling or burning sensation in the skin), was reported in approximately one in five participants on the 12 mg arm in TRIUMPH-4 ^[14]. The mechanism is under investigation. Class-typical signals familiar from other incretin-pathway molecules — gallbladder events, rare pancreatitis, modest heart-rate elevation, and the gastrointestinal intolerance that accompanies dose escalation — have all appeared in the trial record at expected magnitudes ^[8][9].

No data exist in pregnancy, lactation, pediatric populations, or in patients with severe renal or hepatic impairment. The molecule's effects on lean mass and body composition are still being characterized, with particular attention to the glucagon arm's theoretical effects on hepatic amino acid handling.

How to read this site

The trial record is laid out across five reading pages. /research walks through mechanism, the four Phase 2 readouts, and the Phase 3 program as it currently stands. /dosage covers the dose ranges that were studied, the titration schedules used in the trials, and the pharmacokinetics that justify a weekly schedule. /faq answers the questions visitors most often arrive with — prescribing, compounding, comparison with dual-agonist molecules, and timing of likely approval. /references gives full citations with DOIs and PubMed links. /about is the masthead — who publishes this site and on what terms.

This is a reading room. It does not sell anything. It does not have a referral arrangement with any pharmacy, clinic, telehealth provider, or research-chemical vendor. The disclaimer at the bottom of every page is the contract.