Retatrutide is the drug people mean when they talk about a “triple agonist.” It is a single peptide, injected once a week in its trials, built to switch on three hormone receptors at once. The weight losses in its phase 2 trial made it widely searched well before any approval. What follows is what its trials measured, and what they have not yet shown. It sits under the weight goal.
What “triple agonist” means
Semaglutide acts on one receptor, GLP-1. Tirzepatide acts on two, GLP-1 and GIP. Retatrutide is a single peptide that acts on those two and adds a third, the glucagon receptor. [1]
The glucagon arm is the new idea, and it is also where the mechanism is still a hypothesis. The phase 2 papers report what happened to weight, blood sugar and heart rate, but they were not designed to show how much of the extra effect comes from glucagon rather than from the other two receptors. For how the two-receptor and one-receptor drugs compare, see tirzepatide vs semaglutide.
The phase 2 obesity trial
The trial that drew attention randomized 338 adults with obesity, or overweight plus a weight-related condition, to weekly retatrutide or placebo for 48 weeks [1]. The trial used maintenance doses of 1 mg, 4 mg, 8 mg and 12 mg, some reached from a lower starting dose.
At 48 weeks, mean weight fell 8.7% on 1 mg, 17.1% on 4 mg, 22.8% on 8 mg and 24.2% on 12 mg, against 2.1% on placebo. At the 12 mg dose, 83% of participants lost at least 15% of their weight, against 2% on placebo [1].
The costs followed the dose too. Gastrointestinal side effects were the most common, rose with dose, and were partly reduced by starting at 2 mg rather than 4 mg. Heart rate rose with dose, peaked at 24 weeks and then declined [1]. That heart rate signal is one of the things a larger trial has to settle.
In type 2 diabetes
A phase 2 trial in 281 adults with type 2 diabetes compared retatrutide with placebo and with dulaglutide, an older GLP-1 drug [2]. At 24 weeks, HbA1c fell 2.02 percentage points on the 12 mg dose, against 0.01 on placebo and 1.41 on dulaglutide. At 36 weeks, weight fell 16.94% on 12 mg, against 3.00% on placebo.
The first phase 3 result is also in diabetes. TRANSCEND-T2D-1 randomized 537 adults whose diabetes was not controlled by diet and exercise, and gave 4 mg, 9 mg or 12 mg weekly, or placebo, for 40 weeks [3]. HbA1c fell 1.94 points on 12 mg, against 0.81 on placebo, and weight fell 15.3% against 2.6%. Between 2% and 5% of people on retatrutide stopped treatment because of side effects, against none on placebo.
Where the obesity trials stand
The obesity program is called TRIUMPH. Its design paper describes four phase 3 trials with more than 5,800 participants, testing weight loss and, nested within them, sleep apnea and knee osteoarthritis, plus one trial in people with cardiovascular disease [4]. ClinicalTrials.gov lists TRIUMPH-1, with 2,335 participants, as completed in April 2026 [6]. Those are the results an approval decision would rest on.
Is retatrutide FDA-approved?
No. Drugs@FDA lists no application for retatrutide, and in June 2026 its maker posted a pre-approval expanded-access listing that describes it as investigational [5]. That listing is narrow: single patients with a BMI of 35 or more and at least two serious or life-threatening obesity complications, who have not responded to approved therapy and cannot join a trial.
Retatrutide is also on none of the FDA’s lists of bulk substances nominated for compounding [8]. For what that means in practice, see are peptides legal.
What this means for you
In phase 2, retatrutide produced large, dose-dependent weight loss, and a phase 3 diabetes trial has found it lowers weight and blood sugar against placebo. It is still unapproved, and no human dose outside a trial has been established. For the peptides with approvals and published trials, see which peptides for weight loss have human trials, or the daily tablet in what the Wegovy pill trials showed.