In trials, retatrutide was given once a week at doses from 0.5 to 12 mg, and phase 3 tested three target doses: 4, 9 and 12 mg. The highest dose, 12 mg, cut body weight by 25.0 percent after 80 weeks. The 4 mg dose gave 17.6 percent with clearly fewer stomach complaints. Below we compare all the doses from five trials, the way they were increased and what each of them achieved.
Which retatrutide doses were tested in trials?
The phase 2 trials tested a wide range of doses to find the best balance between effect and tolerability. On that basis Lilly chose three doses for phase 3. The authors of the phase 2 trial in people with diabetes state plainly that its results were used to select the phase 3 doses.
| Trial | Who took part | Weekly doses | Duration |
|---|---|---|---|
| Phase 2, obesity | 338 people without diabetes | 1, 4, 8 and 12 mg | 48 weeks |
| Phase 2, type 2 diabetes | 281 people | 0.5, 4, 8 and 12 mg | 36 weeks |
| TRIUMPH-1 | 2339 people without diabetes | 4, 9 and 12 mg | 80 weeks |
| TRIUMPH-2 | 1152 people with diabetes | 4, 9 and 12 mg | 80 weeks |
| TRANSCEND-T2D-1 | 537 people with diabetes | 4, 9 and 12 mg | 40 weeks |
In phase 3 the 4 mg dose was tested only in TRIUMPH-1, TRIUMPH-2 and TRANSCEND-T2D-1. The TRIUMPH-3 and TRIUMPH-4 trials include only the 9 and 12 mg doses.
How was the dose increased at the start?
The dose was increased gradually, because a start that was too fast worsened gastrointestinal complaints. In the phase 2 obesity trial, the group with a 12 mg target dose started at 2 mg. It then received 4 mg, 8 mg and finally 12 mg. This is how the trial record on ClinicalTrials.gov describes the scheme.
The 4 and 8 mg doses were tested with two different starts: from 2 mg or from 4 mg. Comparing these variants gave one of the most important findings of the trial. Starting at 2 mg partly reduced stomach complaints compared with starting at 4 mg.
In phase 3 the whole dose-escalation period lasted 16 weeks, followed by 64 weeks on a fixed dose. The protocol allowed a permanent dose reduction when stomach complaints did not ease despite other measures. Before that, a temporary reduction and a renewed increase had to be tried. Lilly has not published the individual escalation steps for phase 3, so we do not give them here.
What did each dose achieve in people without diabetes?
In people without diabetes every higher dose gave a greater weight loss. This is clearest when comparing 4 mg with 9 and 12 mg. The difference between 9 and 12 mg was much smaller, as the table shows well.
| Dose | Phase 2, after 48 weeks | TRIUMPH-1, after 80 weeks |
|---|---|---|
| 1 mg | 8.7 percent | not tested |
| 4 mg | 17.1 percent | 17.6 percent |
| 8 mg | 22.8 percent | not tested |
| 9 mg | not tested | 23.7 percent |
| 12 mg | 24.2 percent | 25.0 percent |
| Placebo | 2.1 percent | 3.9 percent |
Moving from 4 to 9 mg gave about 6 percentage points more in TRIUMPH-1. Moving from 9 to 12 mg gave only 1.3 points more. The 4 mg dose after 80 weeks gave a result very close to that after 48 weeks in phase 2.
What did each dose achieve in people with type 2 diabetes?
In people with diabetes a higher dose also gave a greater fall in weight and blood sugar. In TRANSCEND-T2D-1 retatrutide was the participants' only glucose-lowering medicine. Glycated haemoglobin, the average blood sugar over recent months, fell clearly more than on placebo at every dose.
| Dose | HbA1c fall after 40 weeks | Weight loss after 40 weeks | Weight loss after 80 weeks in TRIUMPH-2 |
|---|---|---|---|
| 4 mg | 1.69 points | 11.5 percent | 11.9 percent |
| 9 mg | 1.86 points | 13.9 percent | 16.8 percent |
| 12 mg | 1.94 points | 15.3 percent | 18.8 percent |
| Placebo | 0.81 points | 2.6 percent | 5.1 percent |
In the phase 2 diabetes trial and in TRANSCEND-T2D-1 no severe hypoglycaemia, a dangerous fall in blood sugar, was recorded. In TRIUMPH-2 weight loss after 80 weeks was smaller than in TRIUMPH-1 at every dose. The difference ranged from 5.7 percentage points at 4 mg to 6.9 points at 9 mg.
How did the dose affect tolerability?
Gastrointestinal complaints were the most common side effect and rose with the dose. This is shown most precisely by TRIUMPH-2, which reports figures for each dose separately.
| TRIUMPH-2, 80 weeks | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 14 percent | 21 percent | 28 percent | 8 percent |
| Diarrhoea | 27 percent | 34 percent | 34 percent | 13 percent |
| Permanent stop of treatment | 4 percent | 12 percent | 8 percent | 5 percent |
At 4 mg treatment was stopped as rarely as on placebo. In TRANSCEND-T2D-1 stops due to side effects ranged from 2 to 5 percent, and complaints eased over time. In the phase 2 diabetes trial stomach complaints affected 13 percent of people at 0.5 mg and 50 percent with a fast start to 8 mg.
In TRIUMPH-1 at the highest dose, 42.4 percent of participants reported nausea and 32.0 percent diarrhoea. The Pharmaceutical Journal reported these figures in its coverage of the phase 3 results. Stops due to side effects ranged there from 4.1 to 11.3 percent, against 4.9 percent on placebo.
How much does a week cost at each dose?
The cost of a week depends directly on the dose, because the shop price works out per milligram. A 20 mg vial of retatrutide costs 200 EUR, so 10 EUR per milligram. The 40 mg pen costs 350 EUR, so 8.75 EUR per milligram. The table converts this into a week at the phase 3 doses.
| Weekly dose | 20 mg vial, cost per week | 40 mg pen, cost per week | How many weeks a 40 mg pen lasts |
|---|---|---|---|
| 4 mg | 40 EUR | 35 EUR | 10 weeks |
| 9 mg | 90 EUR | 78.75 EUR | over 4 weeks |
| 12 mg | 120 EUR | 105 EUR | over 3 weeks |
At higher doses the pen saves 1.25 EUR on every milligram. Supplies for the whole escalation period are calculated in the guide on how long a GLP-1 vial lasts. The differences between a pen and a vial are described in the guide peptide pen vs powder vial.
Where to buy retatrutide?
In the shop, retatrutide comes in three versions from three manufacturers. Retatrutide 20 mg Bio-Peptide costs 200 EUR and is in stock. Retatrutide 20 mg Genheal costs 200 EUR and is available on backorder. Retatrutide 40 mg Nouveaux in a pen costs 350 EUR and is in stock.
The doses described above come from clinical trials and are not a recommendation for research material. Retatrutide is not an approved medicine, and choosing a dose for a person is a matter for a doctor. How to convert a dose in milligrams into syringe marks is shown in the guide on converting a peptide dose to syringe units. The course of weight loss over the months is described in the guide on retatrutide results, and all versions are on the retatrutide page.
Frequently asked questions
Which retatrutide doses were tested in phase 3?
TRIUMPH-1, TRIUMPH-2 and TRANSCEND-T2D-1 tested doses of 4, 9 and 12 mg once a week. TRIUMPH-3 and TRIUMPH-4 include only 9 and 12 mg.
What dose was retatrutide started at?
In the phase 2 trial, the group with a 12 mg target dose started at 2 mg and went through 4 and 8 mg. In phase 3 the dose escalation took 16 weeks.
Which retatrutide dose gave the greatest weight loss?
The 12 mg dose, which cut body weight by 25.0 percent after 80 weeks in TRIUMPH-1. The 9 mg dose gave 23.7 percent and 4 mg gave 17.6 percent.
Is a lower dose better tolerated?
Yes, in TRIUMPH-2 nausea affected 14 percent of people at 4 mg and 28 percent at 12 mg. Stops of treatment at 4 mg were as rare as on placebo.
How much does a week of retatrutide cost at 12 mg?
From a 20 mg vial at 200 EUR it comes to 120 EUR a week, and from a 40 mg pen at 350 EUR to 105 EUR a week.
Sources
- Jastreboff AM, Kaplan LM, Frías JP et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. New England Journal of Medicine, 2023, 389(6): 514-526. https://doi.org/10.1056/NEJMoa2301972
- Rosenstock J, Frias J, Jastreboff AM et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial conducted in the USA. The Lancet, 2023, 402(10401): 529-544. https://doi.org/10.1016/S0140-6736(23)01053-X
- Jastreboff AM, Kaplan LM, Davies MJ et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine, 2026. https://doi.org/10.1056/NEJMoa2604169
- Bellido V, le Roux CW, Ekinci EI et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). The Lancet, 2026. https://doi.org/10.1016/S0140-6736(26)01861-1
- Bajaj HS, Welch M, Shah P et al. Efficacy and safety of retatrutide in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1). The Lancet, 2026, 407(10546): 2402-2413. https://doi.org/10.1016/S0140-6736(26)00967-0
- Giblin K, Kaplan LM, Somers VK et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism, 2026, 28(1): 83-93. https://doi.org/10.1111/dom.70209
- ClinicalTrials.gov. LY3437943 in Participants Who Have Obesity or Overweight, NCT04881760. https://clinicaltrials.gov/study/NCT04881760
- The Pharmaceutical Journal. Phase III retatrutide study demonstrates 30% weight loss, 2026. https://pharmaceutical-journal.com/article/news/phase-iii-retatrutide-study-demonstrates-30-weight-loss