Biohacking Kompakt

Peptide & Experimental

GLP-3

Experimental triple receptor agonist (GLP-1, GIP, glucagon) · nickname for retatrutide (LY3437943), GLP-1/GIP/glucagon triagonist

GLP-3 is neither a hormone nor a medicine, but a nickname from the weight-loss scene. What is meant is almost always retatrutide, the triple agonist from Eli Lilly that reduced more weight in trials than any active substance before it. What is sold under the GLP-3 label, however, is not the trial product, and first real-world data show exactly this difference.

In short

GLP-3 is the unofficial name for retatrutide, an active substance that binds to three hormone receptors at once: GLP-1, GIP and glucagon. In a phase 2 trial the investigational drug reduced weight by up to 24.2 percent after 48 weeks, and in the large phase 3 trial, according to the manufacturer, by up to 28.3 percent after 80 weeks. It is not yet approved anywhere. In a first, not yet peer-reviewed analysis of patient records, the gray-market products traded as GLP-3 achieved an average weight loss of 7.2 percent after 6 to 12 months, less than half as much as in trial participants, with more cardiovascular complaints.

What it is

There is no hormone called GLP-3. In the body, the precursor molecule proglucagon gives rise to glucagon, GLP-1, GLP-2 and oxyntomodulin, nothing more. The name is a coinage of the scene and alludes to the three hormone receptors on which the active substance acts. Press reports since late 2025 consistently describe GLP-3 as an informal nickname for retatrutide.

Retatrutide, development code LY3437943, comes from Eli Lilly and is currently going through the final approval trials. Offered under the name GLP-3, by contrast, are products from peptide dealers, usually with the note that they are intended for research purposes only. Whether they really contain retatrutide, and in what amount and purity, is checked by no one.

How quickly this market is spreading is shown by patient records from the US: between October 2023 and March 2026, the number of retatrutide users outside trials grew 1.8-fold per quarter. The products were obtained mainly via online and telehealth providers, 57.4 percent, and via compounding pharmacies, 29.4 percent. The US Food and Drug Administration (FDA) has since sent warning letters to such providers.

How it is supposed to work

The active substance combines three signals. Via the GLP-1 receptor it dampens appetite, delays gastric emptying and enhances insulin release after eating, the principle of semaglutide. The GIP component adds to the insulin effect, the principle of tirzepatide. New is the third arm at the glucagon receptor, which is supposed to stimulate energy expenditure and fat breakdown in the liver.

How much each arm contributes to the overall effect has not been studied separately in humans. The result is visible: a large weight loss and a particularly marked decrease in liver fat.

What the investigational drug can do

In the 2023 phase 2 trial with 338 adults with obesity, participants at the highest dose level lost an average of 24.2 percent of their weight after 48 weeks, under placebo 2.1 percent. In a subgroup with fatty liver, liver fat fell by up to 82.4 percent after 24 weeks; in up to 86 percent it was then in the normal range. A phase 3 trial in type 2 diabetes with 537 participants confirmed the lowering of blood sugar in 2026.

According to the manufacturer’s announcement of May 2026, the large phase 3 trial TRIUMPH-1 with 2,339 participants showed up to 28.3 percent weight loss after 80 weeks versus 2.2 percent under placebo. In July 2026, Lilly reported two further successful phase 3 trials over 80 weeks: TRIUMPH-2 with 1,152 adults with type 2 diabetes and overweight or obesity (up to 20.8 versus 4.0 percent) and TRIUMPH-3 with 1,949 adults with severe obesity and cardiovascular disease (up to 22.6 versus 3.2 percent). Peer-reviewed publications on these are still pending. Lilly intends to submit the application for approval in the US in the first quarter of 2027.

What users report

A not yet peer-reviewed analysis of Reddit posts up to December 2025 found 13,589 users who reported their own use. Most frequently they described not gastrointestinal complaints as in the trials, but increased appetite, fatigue, more energy, nausea, cravings, insomnia and an elevated heart rate. In press reports, users tell of large weight losses, but also of abnormal skin sensations.

The authors explicitly call their results hypothesis-generating. That users sometimes report more rather than less hunger does, however, fit with the real-world data, according to which the gray-market products work less strongly than the trial product.

What is well supported

The principle of action behind the name is excellently supported. Triple agonism at the GLP-1, GIP and glucagon receptors achieved up to 24.2 percent weight loss after 48 weeks in a double-blind phase 2 trial, and in phase 3, according to the manufacturer, up to 28.3 percent after 80 weeks, plus a strong decrease in liver fat and a lowering of blood sugar in type 2 diabetes.

There are now also first human data on the gray-market products. An analysis of electronic patient records from a US network with 29 million patients found 531 users with a traceable source, 71.2 percent of them outside trials, mainly via online providers. These users lost an average of 7.2 percent after 6 to 12 months. So the products work, just considerably less strongly than expected.

What the studies show

Murugadoss et al. 2026 — gray market versus trial (preprint)

Observational study based on electronic patient records, not peer-reviewed. Use of retatrutide outside trials grew 1.8-fold per quarter. In the matched comparison, trial participants lost 15.5 percent after 6 to 12 months, gray-market users 7.2 percent and tirzepatide users 7.7 percent. Gray-market users had more cardiovascular and neuropsychiatric complaints than comparison groups.

Jastreboff et al. 2023 — phase 2 in the New England Journal

Double-blind, placebo-controlled, 338 adults with obesity, 48 weeks. Primary endpoint met after 24 weeks, up to 17.5 versus 1.6 percent, after 48 weeks up to 24.2 versus 2.1 percent. Side effects mainly gastrointestinal, dose-dependent, plus an increase in heart rate peaking after 24 weeks.

TRIUMPH-1 2026 — phase 3 (manufacturer data)

Randomized, double-blind, 2,339 participants, 80 weeks. Up to 28.3 percent weight loss versus 2.2 percent under placebo, nausea up to 42.4 percent, discontinuation due to side effects up to 11.3 percent. So far published only as an announcement by Eli Lilly.

TRIUMPH-2 and TRIUMPH-3 2026 — phase 3 (manufacturer data)

Both randomized, each 80 weeks. TRIUMPH-2 with 1,152 adults with type 2 diabetes and overweight or obesity: up to 20.8 percent weight loss versus 4.0 percent under placebo; HbA1c fell by up to 1.6 percentage points, under placebo by 0.2. TRIUMPH-3 with 1,949 adults with severe obesity and existing cardiovascular disease: up to 22.6 percent versus 3.2 percent. Discontinuation due to side effects up to 11.6 and 13.5 percent respectively, versus 4.9 and 4.8 percent under placebo. So far published only as an announcement by Eli Lilly of July 23, 2026.

Where the data stop

For the products labeled GLP-3 there is no controlled study. The two analyses of gray-market users are observational data and self-reports, both not yet peer-reviewed, and neither of them knows what was actually in the vials. An independent analysis of 6,441 samples from 14 gray-market peptides, including retatrutide, found fundamental quality defects in 41.6 to 71.1 percent, depending on the criterion, and measurable endotoxin in 15 percent. The halved effect in real-world use fits with underdosed or contaminated products; this has not been proven.

For the investigational drug, too, the peer-reviewed phase 3 publications, data on the period after discontinuation and a direct comparison with tirzepatide are still missing.

Status, approval and legal

Retatrutide is not approved in Germany, the EU or the US; the manufacturer plans to submit the application for approval in the US in the first quarter of 2027. What is sold as GLP-3 is not a marketable medicine in Germany. The FDA has excluded retatrutide from compounding, sent warning letters to online providers and warned about products that are falsely labeled as research products and sold to consumers with directions for use. In sport, retatrutide falls under S0 of the WADA list as a non-approved substance and is prohibited at all times; a detection method has been published. We do not give dosage information for non-approved substances.

Safety

With the investigational drug, gastrointestinal complaints are the most common side effects, above all nausea: in TRIUMPH-1, up to 42.4 percent had nausea versus 14.8 percent under placebo, and up to 12.5 percent reported abnormal skin sensations. Heart rate rises. In gray-market users, the patient records showed cardiovascular and neuropsychiatric complaints more frequently than in users of approved drugs. A 2026 case report describes a man with type 1 diabetes who developed severe ketosis with acute kidney failure after retatrutide bought online and a gastrointestinal infection; the active substance has no established role in type 1 diabetes. The FDA warns that counterfeit products may contain the wrong active substance, too little, too much or none at all. Data on pregnancy and long-term safety are missing.

BK-Score Hype far ahead of evidence

Human evidence2
Mechanism8
Safety data1
Hype gap1
Track record of use4

Here the distinction between principle of action and product is decisive: what is rated is the gray-market product sold as “GLP-3”, not Eli Lilly’s pharmaceutical retatrutide. The principle, triple agonism at the GLP-1, GIP and glucagon receptors, is very well supported in humans: retatrutide achieved up to 24.2 percent weight loss after 48 weeks in phase 2 (Jastreboff 2023) and, according to the manufacturer, up to 28.3 percent after 80 weeks in TRIUMPH-1 with 2,339 participants, up to 20.8 percent in TRIUMPH-2 in type 2 diabetes and up to 22.6 percent in TRIUMPH-3 in severe obesity with cardiovascular disease; that is why the mechanism scores high; the rating of the active substance can be found in the entry on retatrutide. A hormone called GLP-3 does not exist, the name is a nickname from the scene, and the product is neither batch-controlled nor identical to the investigational drug. There are now first human data on it, both not peer-reviewed: in US patient records, gray-market users lost an average of 7.2 percent after 6 to 12 months, trial participants 15.5 percent, with more cardiovascular complaints (Murugadoss 2026), and a Reddit analysis counted 13,589 users (Sehgal 2026). Use is therefore widespread and growing; there is no controlled study or safety assessment for the product.

The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless. “Track record of use 9” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about GLP-3

What is GLP-3?

GLP-3 is not a hormone but a nickname used in the scene for retatrutide, an active substance that acts on the receptors for GLP-1, GIP and glucagon. Officially, there are only GLP-1 and GLP-2.

Is GLP-3 the same as retatrutide?

What is meant is usually retatrutide. Whether the products sold under the name GLP-3 actually contain retatrutide in the stated amount and purity, however, is checked by no one.

How much weight do you lose with retatrutide?

In the phase 2 trial up to 24.2 percent after 48 weeks, in phase 3 according to the manufacturer up to 28.3 percent after 80 weeks. In a first real-world analysis, gray-market users lost an average of 7.2 percent after 6 to 12 months.

Is GLP-3 stronger than tirzepatide?

There is no direct comparison in a trial. In real-world use, gray-market users in a first analysis lost about as much weight as tirzepatide users, considerably less than trial participants.

When will retatrutide be approved?

Eli Lilly plans to submit the application for approval in the US in the first quarter of 2027. In Germany and the EU it is not yet approved.

What side effects does GLP-3 have?

With the investigational drug, mainly gastrointestinal complaints such as nausea, plus an increase in heart rate and abnormal skin sensations. With gray-market products, unverified quality is added and, in patient records, more frequent cardiovascular complaints.

Related

Sources

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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-30.