Retatrutide

Retatrutide has the strongest human evidence of anything in this library, and it is not close. Most entries here rest on mice, cell culture, or a handful of uncontrolled pilot studies. This one rests on a completed Phase 3 program in thousands of people, with published results, prespecified endpoints, and a placebo arm.

The headline is the weight loss, and it is genuinely large: roughly a quarter of body weight at 80 weeks on the higher doses, up to about 30 percent at 104 weeks in the arm escalated to maximum tolerated dose. But the part that gets skipped is more interesting. Blood pressure, triglycerides, non-HDL cholesterol and hsCRP all moved in the right direction, liver fat dropped in the MASLD substudy, and knee osteoarthritis pain improved. That is not a weight-loss drug. That is a metabolic drug whose most visible output happens to be weight.

What it is not is available, or approved, or free. Lilly has said it intends to file in 2027. Until then every gram in circulation came from somewhere the FDA has not inspected, and the side-effect profile is real enough that one in nine people at the top dose quit the trial over it.

Retatrutide, called LY3437943 in the earlier literature, is a single engineered molecule that activates three different receptors: GLP-1, GIP, and glucagon. Semaglutide hits one of those. Tirzepatide hits two. This hits all three, which is why it gets called a triple agonist.

Worth being precise about a thing your friends will get wrong: it activates the glucagon receptor, it does not block anything. The whole class works by turning signalling up, not by occupying a receptor to keep something else out. That distinction matters when you get to the craving and addiction research further down, because the popular explanation of how these drugs quiet cravings has the direction backwards.

Why Three Receptors Instead of One

Each arm does a different job, and the combination is the point.

GLP-1 is the one everyone knows. It slows gastric emptying, increases satiety, and improves glucose-dependent insulin release. This is the appetite arm, and on its own it produces the 15 percent weight loss that made semaglutide famous.

GIP is the one most conversations skip. GIP receptor agonism improves insulin sensitivity and changes how adipose tissue handles nutrient load. Adding it to GLP-1 is most of the difference between semaglutide and tirzepatide.

Glucagon is the novel and genuinely risky arm. Glucagon raises energy expenditure and drives hepatic fat mobilisation, which is why the liver-fat results are as strong as they are. It also raises hepatic glucose output, which is the obvious thing that could go wrong, and is why the glycemic data in the diabetes trials mattered more than the weight data.

Where That Leads

Two of the three arms independently improve insulin sensitivity, and the third mobilises the ectopic fat that drives insulin resistance in the first place. So the metabolic effects are not a bonus that comes along with losing weight. They are what the molecule is doing, and the weight is downstream of it.

The overreach on this compound is not usually about the weight loss. It is about extending a real metabolic result into diseases the drug has never been tested against.

The Alzheimer's leap is the clearest example, and it just got tested. The reasoning sounds airtight: insulin resistance is implicated in Alzheimer's, GLP-1 drugs improve insulin sensitivity, therefore GLP-1 drugs should help Alzheimer's. That hypothesis went into the largest trial anyone has run on it. EVOKE and EVOKE+ randomised 3,808 people with early Alzheimer's to oral semaglutide or placebo. It missed. No benefit over placebo on CDR-SB, and the extension period was discontinued. CSF biomarkers improved by up to 10 percent and cognition did not follow, which is about as clean a demonstration as you will get that a mechanism moving is not a disease changing. Anyone still selling you the Alzheimer's angle either has not read it or is hoping you have not.

The addiction angle is the opposite case, and it is holding up. GLP-1 receptor agonism reduces alcohol craving and heavy drinking in randomised trials. A 2025 phase 2 RCT found lower craving, lower drinking quantity and fewer heavy drinking days on low-dose semaglutide, including measurably less alcohol consumed in a laboratory setting. A 2026 trial randomised 108 treatment-seeking patients with alcohol use disorder and comorbid obesity to semaglutide 2.4 mg or placebo on top of CBT, and found a 13.7 percentage point greater reduction in heavy drinking days. The likely mechanism is GLP-1 receptor signalling in the mesolimbic reward pathway, not receptor blockade. The catch: every one of those trials used semaglutide. Retatrutide has not been tested for this at all, and a triple agonist is not interchangeable with a single one just because they share an arm.

Dose extrapolation is the quiet one. The trial doses were reached by slow escalation with clinical monitoring, and the discontinuation rate still climbed with every step up. Starting where a trial finished is how people produce side effects the trial did not.

The adverse events are well characterised, which is itself a luxury on this site, and they are not trivial.

Gastrointestinal effects dominate and scale with dose. Across the 4, 9 and 12 mg arms: nausea in 28.6, 38.4 and 42.4 percent, diarrhoea in 25.2, 34.1 and 32.0 percent, constipation in 23.8, 25.9 and 26.1 percent, vomiting in 10.6, 22.8 and 25.3 percent. Most of it lands during escalation and is mild to moderate.

Discontinuation because of adverse events tracks the same way: 4.1 percent at 4 mg, 6.9 percent at 9 mg, 11.3 percent at 12 mg, against 4.9 percent on placebo. At the top dose roughly one person in nine stopped over side effects. That is the number to hold next to the 25 percent weight loss, because they came from the same arm.

Heart rate rose in a dose-dependent way, peaking around 24 weeks before declining, consistent with the class. Pre-existing tachyarrhythmia is a reason for closer monitoring. Mild to moderate dysesthesia was reported, along with upper respiratory and urinary tract infections, with most of the urinary and neurological cases resolving during treatment.

None of this was measured on grey-market material, and none of it was measured without a physician watching.

If you are trying to work out whether this compound deserves your attention, the honest answer is that it deserves more of it than most things discussed in the same breath, and that attention should mostly be patience.

What the evidence supports: retatrutide produces the largest weight reduction yet demonstrated in a Phase 3 obesity trial, and it improves blood pressure, lipids, inflammatory markers and liver fat alongside it. The metabolic improvements are mechanistically driven, not merely a side effect of being lighter.

What the evidence does not yet support: any claim about cardiovascular events, dementia, addiction, longevity, or anything else that has not been an endpoint in a trial. And nothing at all about what unregulated material does, because that has never been studied and never will be.

The realistic move for most people reading this is to know what it is, know the filing is expected in 2027, and know that a prescribed and monitored version of this is a genuinely different proposition from a vial off the internet.

Not an approved medicine. There is no pending application. Lilly stated on 2026-07-23 that it intends to file in 2027. Any page describing retatrutide as approved, or as awaiting approval, is wrong today.

Not a peptide in the sense most of this library uses the word. It is a pharmaceutical-grade engineered agonist from a Phase 3 program, not a research compound with a preclinical file and a hopeful audience.

Not permitted in tested sport. WADA prohibits it at all times under S0, the unapproved-substances class. It is not named on the list, and it does not need to be. Note that semaglutide and tirzepatide markers sit on the 2026 Monitoring Program, which is not the same thing as a prohibition.

Not a treatment for anything it has not been trialled for. Insulin sensitivity improving is a real finding. It is not a licence to attach the compound to every disease in which insulin resistance appears.

This is the entry I would point a friend at first, and it is worth saying why, because it is not the compound I find most interesting.

Most of this library is me trying to be fair to compounds that have promising biology and almost no human data. That takes a lot of hedging, and I know how the hedging reads. Retatrutide is the entry where the hedging mostly comes off, and it should, because the evidence earned that. When a Phase 3 trial with a placebo arm shows a quarter of body weight gone and blood pressure down 14 points, I am not going to write about it in the same cautious register I use for a compound whose entire file is mice.

That is the standard I want applied across every page here. Confidence should track evidence, in both directions. If everything on a site sounds equally careful, then the careful language has stopped carrying information, and the reader has no way to tell the well-supported thing from the hopeful one.

Where I stay firm: I am not going to tell you to take this, I am not going to publish doses, and I am not going to pretend a vial bought online is the thing that was studied. Those are not compliance reflexes. Every number on this page came out of a supervised trial using material somebody verified, and detaching the results from the conditions that produced them is the single most common way this category misleads people.