Retatrutide + Tesamorelin
One has five positive Phase 3 trials and no approval. The other is approved for a condition you almost certainly do not have.
Retatrutide is the most effective weight loss compound ever tested and it is not licensed anywhere on earth. Tesamorelin is licensed, narrowly, for reducing deep belly fat in people with HIV-related fat redistribution. It gets added here to target visceral fat, which is a job retatrutide already does hard.
Five positive Phase 3 trials, and bariatric-surgery numbers.
TRIUMPH-1 enrolled 2,339 adults for 80 weeks. Average weight loss at the top dose reached 28.3% among people who stayed on treatment, and 25.0% counting everyone who started.[1]
In an extension running to 104 weeks in people who started with a BMI of 35 or higher, average loss reached 30.3%, with no sign of levelling off.[2] At the top dose in TRIUMPH-1, 45.3% of participants lost at least 30% of their body weight and 65.3% finished with a BMI under 30.
Four more Phase 3 trials read the same way. TRIUMPH-2 in type 2 diabetes, 1,152 adults, up to 20.8% against 4.0% on placebo.[3] TRIUMPH-3 in 1,949 adults with severe obesity and established heart disease, up to 22.6% against 3.2%.[3] TRIUMPH-4 in knee osteoarthritis, up to 28.7%, alongside a pain reduction of about 4.5 points.[4]
Lilly plans to file for US approval in the first quarter of 2027.[3] Until that completes, retatrutide is approved by no regulator anywhere, and everything sold online is research chemical material.
Tesamorelin is added for a job retatrutide already does.
The case for this stack is that the two compounds attack different fat. Retatrutide takes weight off generally, and tesamorelin goes after visceral fat, the deep kind packed around the organs that ordinary weight loss reaches last.
That argument would hold against a plain GLP-1. It holds much less well against retatrutide, and the reason is the third receptor. Glucagon agonism drives fat out of the liver and the abdominal cavity specifically, and it is what separates retatrutide from tirzepatide and semaglutide.
A substudy measured it directly. In people with fatty liver disease, retatrutide cut liver fat by 81.4% at one dose and 82.4% at the next, against a 0.3% increase on placebo. At the top dose, 86% of participants finished with liver fat in the normal range. On placebo, nobody did.[5]
Waist circumference improved substantially across the Phase 3 trials as well.[6] So the compound being added to reach visceral fat is being added to a compound that already strips it harder than anything else tested.
Whether tesamorelin adds anything measurable on top of that has never been studied. The stack rests on an argument built for a weaker partner than the one it is now paired with.
Tesamorelin is licensed, for something specific.
Tesamorelin has genuine FDA approval, which makes it rare in this catalogue. The approval is for reducing excess abdominal fat in adults with HIV-associated lipodystrophy, a condition in which fat redistributes in a particular pattern.
It is not approved as a general anti-visceral-fat drug, and vendor pages routinely quote the approval without the indication attached. An approval describes a population and an outcome, and detaching it from either turns it into marketing.
The other thing worth knowing is what tesamorelin is. It works by raising your own growth hormone, which means it shares a mechanism with every growth hormone stack on this site. Anyone already running CJC-1295 or sermorelin alongside this is opening the same door twice.
Both compounds move it, in opposite directions.
Retatrutide improves blood sugar control. In TRIUMPH-2, adults with type 2 diabetes saw A1C fall by an average of 1.4 to 1.6 percentage points from a starting point of 7.7%. A1C is a blood test showing average blood sugar over the previous few months.[3]
Growth hormone pushes the other way. Raising it reduces insulin sensitivity, which is a consistent finding across the growth hormone compounds and the reason MK-677's glucose effect is replicated across every trial that measured it.
So this stack contains one compound lowering blood sugar and one working against that. Nobody has measured what happens when both run together, and it is the specific thing worth watching if anyone does.
Discontinuation because of side effects in the retatrutide Phase 2 trial ran from 6% to 16%, rising with dose.[7] That is the compound on its own, before anything is added to it.
Four in ten had nausea. One in nine stopped.
TRIUMPH-1 had 2,339 participants and a placebo group, meaning people given a dummy injection with nothing active in it, so these rates come with a comparison. At the top dose:
| Effect | Retatrutide, top dose | Placebo |
|---|---|---|
| Nausea | 42.4% | 14.8% |
| Diarrhoea | 32.0% | 13.5% |
| Constipation | 26.1% | 10.9% |
| Vomiting | 25.3% | 4.8% |
| Dysaesthesia, an odd burning or prickling feeling in the skin | 12.5% | 0.9% |
| Stopped because of side effects | 11.3% | 4.9% |
Most of the stomach and gut effects appear in the first week or two after each dose increase and settle over about four to six weeks.[9] The dysaesthesia is less familiar and shows up at roughly fourteen times the placebo rate.[10]
One effect belongs to the glucagon receptor specifically. Heart rate rose by around 6.7 beats per minute at the top dose, climbing with each dose step and peaking near week 24 before easing.[9] The same measure on tirzepatide and semaglutide runs roughly one to four beats. A few participants had supraventricular arrhythmias and conduction disturbances, none of them serious, and serious adverse events overall ran at about 4% in both the retatrutide and placebo groups.[11]
The heart rate signal matters more here than on a page about retatrutide alone, because tesamorelin raises growth hormone and growth hormone causes the body to hold sodium and water. Nobody has measured the two together.
People buying it online report different symptoms than trial participants.
A 2026 analysis went through Reddit posts from retatrutide and peptide communities, identified 13,589 people describing current use, and mapped symptoms for 7,823 of them using a standard medical dictionary.[12]
What they reported does not look like the trials.
- Nausea
- Diarrhoea
- Constipation
- Vomiting
- Decreased appetite
- Increased appetite
- Fatigue
- Increased energy
- Insomnia
- Raised heart rate
Appetite runs the wrong way. Trials record decreased appetite as a common effect, since suppressing appetite is how the drug works. Online users report appetite increase as their single most common symptom, at 17.1%.[10]
Several things could produce that gap and the study cannot separate them. Grey market material may be underdosed, mislabelled or something else entirely. Online reporting is self-selected and nobody is checking. Trial participants answer structured questions while forum users write about whatever stands out. The authors describe their findings as hypothesis-generating and call for pharmacovigilance attention.[12]
The practical point is narrower and firm. The safety profile in the trials describes a known quantity given at a known dose under supervision. Anyone assembling this stack from research chemical vendors is not in that population, and the one study that looked at that population found it reporting something else.
What people ask about this stack
How much weight does retatrutide cause people to lose?
In TRIUMPH-1, 2,339 adults over 80 weeks, the top dose produced an average of 28.3% among people who stayed on treatment and 25.0% counting everyone who started. In a 104-week extension limited to people with a BMI of 35 or higher, it reached 30.3%. For comparison, tirzepatide reached 22.5% in SURMOUNT-1 and semaglutide 20.7% in STEP UP, in their own separate trials.
Is retatrutide approved?
No, nowhere in the world. Five Phase 3 trials have reported positive results and Lilly plans to file for US approval in the first quarter of 2027. Everything sold online today is unapproved research chemical material, whatever the trial results say.
Does adding tesamorelin help with belly fat?
Nobody has tested the combination, and the reasoning behind it is weaker than it looks. Tesamorelin targets visceral fat, and retatrutide already attacks it hard through its glucagon receptor activity, which is the component semaglutide and tirzepatide lack. A liver fat substudy found retatrutide cutting liver fat by more than 80%, with 86% of participants reaching a normal level at the top dose against nobody on placebo.
What is tesamorelin actually approved for?
Reducing excess abdominal fat in adults with HIV-associated lipodystrophy. That is the whole indication. It is not approved as a general fat loss drug, and vendor pages quoting the approval without naming the population are leaving out the part that defines it.
Do the two interact?
On blood sugar, in opposite directions. Retatrutide improves glycemic control, cutting A1C by 1.4 to 1.6 points in adults with type 2 diabetes. Raising growth hormone reduces insulin sensitivity. No study has measured what happens when both run at once, and that is the specific thing to watch. Compare against the other stacks.
What are retatrutide's side effects?
In TRIUMPH-1 at the top dose, against placebo: nausea 42.4% versus 14.8%, diarrhoea 32.0% versus 13.5%, constipation 26.1% versus 10.9%, vomiting 25.3% versus 4.8%. Dysaesthesia, an odd burning or prickling skin sensation, hit 12.5% against 0.9%. Around 11.3% stopped because of side effects against 4.9% on placebo. Heart rate rose about 6.7 beats per minute at the top dose, which is higher than tirzepatide or semaglutide produce and traces to the glucagon receptor.
Why do people online describe different side effects than the trials?
A 2026 analysis of 13,589 people reporting retatrutide use online found their most common symptoms were increased appetite, fatigue, increased energy, insomnia and raised heart rate. The trials are dominated by nausea, vomiting and decreased appetite. Appetite runs opposite between the two. Grey market material may be underdosed or mislabelled, online reporting is self-selected, and nobody is verifying either. The authors call their findings hypothesis-generating.
Is this the same as the aggressive fat loss stack?
It is the two-compound version. The three-compound version adds MOTS-c for metabolic support, which brings a third compound with far less evidence behind it and no data on any combination. The blood sugar question above applies to both.
Every reference carries how it was read.
Retatrutide has a full Phase 3 programme, so most figures here trace to named trials. All were read through company releases and trade reporting rather than the published papers.
- 01TRIUMPH-1, NCT05929066" rel="nofollow noopener" target="_blank">NCT05929066. 2,339 adults, 80 weeks. 28.3% at the top dose among those staying on treatment, 25.0% counting everyone. Also the source for tirzepatide 22.5% in SURMOUNT-1 and semaglutide 20.7% in STEP UP.
- 02TRIUMPH-1 (NCT05929066) extension to 104 weeks in participants with baseline BMI 35 or higher: 30.3% mean loss, 45.3% reaching at least 30% loss, 65.3% reaching BMI under 30.
- 03Eli Lilly news release, 23 July 2026. TRIUMPH-2 (1,152 adults, up to 20.8% against 4.0%, A1C down 1.4 to 1.6 points from 7.7%) and TRIUMPH-3 (1,949 adults, up to 22.6% against 3.2%). BLA submission planned Q1 2027.
- 04TRIUMPH-4 in knee osteoarthritis: 26.4% at 9 mg and 28.7% at 12 mg against 2.1% on placebo, with a WOMAC pain reduction of about 4.5 points.
- 05Randomised phase 2a substudy in metabolic dysfunction-associated steatotic liver disease, 98 participants. PMC11271400. Liver fat change at 24 weeks: minus 81.4% at 8 mg, minus 82.4% at 12 mg, plus 0.3% on placebo. Normal liver fat reached by 86% at 12 mg and 0% on placebo.
- 06Phase 3 secondary endpoints including waist circumference, lipids, blood pressure and hsCRP.
- 07Jastreboff et al., phase 2 obesity trial, New England Journal of Medicine 2023. 24.2% at 12 mg at 48 weeks against 2.1% placebo. Discontinuation for adverse events 6 to 16%, rising with dose.
- 09Side effect comparison across Phase 2, TRIUMPH-4 and TRANSCEND-T2D-1, including the roughly 6.7 bpm heart rate rise at the top dose and the onset and settling pattern of gastrointestinal effects.
- 10TRIUMPH-1 adverse event table against placebo: nausea 42.4% vs 14.8%, diarrhoea 32.0% vs 13.5%, constipation 26.1% vs 10.9%, vomiting 25.3% vs 4.8%, dysaesthesia 12.5% vs 0.9%, discontinuation 11.3% vs 4.9%. Also the 17.1% appetite-increase figure among online users.
- 11Correspondence on retatrutide. PMC10844714. Noting dose-dependent heart rate increases peaking at 24 weeks then declining, non-serious supraventricular arrhythmias and conduction disorders, and serious adverse events at about 4% in both retatrutide and placebo groups.
- 12Self-reported side effects among Reddit users taking nonapproved retatrutide. medRxiv preprint, DOI 10.64898/2026.05.28.26352819. 13,589 users reporting current use, 7,823 with mapped symptoms, classified against MedDRA terms.
- 08Peptide Decoding vendor pricing data, 12 September 2026. Single-compound listings only.