Retatrutide Stacks: What People Combine It With (and What to Avoid)

No retatrutide stack has been tested in people. Of the 33 retatrutide studies on ClinicalTrials.gov as of October 31, 2026, not one combines it with tirzepatide, semaglutide, cagrilintide or any of the peptides people add to it. Even Lilly's first head-to-head result, retatrutide against Ozempic 2 mg in TRANSCEND-T2D-2 (reported October 28), gave each person one drug. The diabetes trials let people stay on drugs like metformin or insulin. Beyond those, the only drugs given alongside it on purpose are a birth control pill, the blood pressure drug metoprolol, and midazolam, warfarin and caffeine, in 3 interaction studies that haven't posted results. Every reta stack you'll find online is assembled from each compound's evidence on its own, and for most of them that evidence is thin.

As of October 31, 2026, retatrutide itself is still investigational. Lilly's October FAQ says it "is not on the market" and that "no one can legally sell it for human use." On filing, Lilly last said, on September 29, 2026, that it plans to submit retatrutide to the FDA in the first quarter of 2027 as a Biologics License Application (BLA). On October 2, 2026, the FDA decided that retatrutide is a drug, not a biological product, so an application would need to be filed under section 505 of the Federal Food, Drug, and Cosmetic Act. Lilly's appeal on that question is pending in the Seventh Circuit, and we found no ruling as of October 31, 2026. More on FDA approval status and whether retatrutide is legal. The add-ons people ask about fall into three groups: other GLP-1 drugs, growth hormone peptides and testosterone for muscle, and a looser set sold for skin, energy and recovery.

The retatrutide stack evidence map

Here's every common add-on in one place, checked on October 31, 2026. The last column is the one that matters most, and not one cell in it says yes.

Sources: ClinicalTrials.gov, the Zepbound, Wegovy and Egrifta WR labels, FDA's testosterone labeling notice (February 2025), FDA's compounding safety-risk page (updated April 22, 2026) and FDA's statement on unapproved GLP-1 drugs (current as of October 1, 2026).

Why people stack reta at all

Mostly to fix something retatrutide does on its own. In TRIUMPH-1, about 4 in 10 people on 12 mg (42.4%) had nausea over 80 weeks, against 14.8% on placebo, and 25.3% vomited, against 4.8%. The other big worry is muscle. In a Phase 2 substudy in people with type 2 diabetes that scanned body composition by DXA, those on 12 mg lost 23.2% of their fat mass in 36 weeks, and Lilly's authors reported that the share of weight lost as lean mass was similar to other obesity treatments. That's 103 people with both scans, so it's a small base.

The rest comes from forums. Reddit threads ask what to stack for muscle gain and how to schedule NAD+ injections, and some describe running reta with tirzepatide. Those are reports, not studies. The side effects themselves, dose by dose, are on the retatrutide side effects page, and the lean mass question has its own page on retatrutide and muscle loss. If nausea is the reason, start with retatrutide nausea. For what people say they're running, with the usual caveat, see the retatrutide Reddit roundup.

Doubling up on GLP-1 drugs

Retatrutide acts on the GIP, GLP-1 and glucagon receptors. Tirzepatide acts on two of those three, and semaglutide on one, so adding either doubles up on a pathway retatrutide already covers.

The labels are direct about it. Zepbound's says "Coadministration with other tirzepatide-containing products or with any glucagon-like peptide-1 (GLP-1) receptor agonist is not recommended." Wegovy's says the same about "any other GLP-1 receptor agonist." Retatrutide's own trials kept these drugs apart too: TRIUMPH-1 excluded anyone who had taken weight loss drugs, including over-the-counter ones, in the 90 days before screening.

Retatrutide and tirzepatide

Lilly is comparing the two in TRIUMPH-5, a Phase 3 trial of about 800 adults where each person gets one drug, not both; its primary completion is estimated for November 2026, and Lilly hadn't released a topline as of October 31. Its liver outcomes trial, SYNERGY-Outcomes, plans to enroll about 4,500 adults with fatty liver disease and also keeps them apart, in separate retatrutide, tirzepatide and placebo arms. On its own, 25% to 29% of people on tirzepatide had nausea across its doses in the Zepbound trials, against 8% on placebo. Why people combine them anyway, and how a switch can overlap the two, is on retatrutide and tirzepatide together. If you're moving from one to the other rather than adding, see switching from tirzepatide; the molecules themselves are compared on retatrutide vs tirzepatide.

Retatrutide and semaglutide

Retatrutide has now been set against semaglutide in a Phase 3 trial, and nobody got both. In TRANSCEND-T2D-2, Lilly randomized 1,298 adults with type 2 diabetes on metformin to retatrutide 9 mg, retatrutide 12 mg or Ozempic 2 mg. At 80 weeks, on the efficacy estimand, people on retatrutide had lost 19.5% (9 mg) and 20.9% (12 mg) of their body weight, against 9.4% on Ozempic. That's Lilly's October 28 release; there's no paper yet, and the 9 mg advantage on A1C was nominal only.

A head-to-head tells you how the two compare, not what happens when you take both. Nausea was close across the arms (21.2% and 23.8% on retatrutide, 21.3% on Ozempic), and for a stack the more telling number is stopping: 7.9% on 12 mg quit over side effects, against 2.7% on Ozempic. For a sense of semaglutide alone in people without diabetes, 44% of people on Wegovy 2.4 mg had nausea in the label trials, against 16% on placebo. At least one person has taken semaglutide without knowing it: the TGA tested a vial sold as retatrutide in Australia and found no retatrutide, only semaglutide at about 8 times the level in approved products. More on retatrutide and semaglutide together and, for diabetes, retatrutide vs Ozempic.

Retatrutide and cagrilintide

Cagrilintide is an amylin analog from Novo Nordisk. ClinicalTrials.gov lists 44 studies with it as an intervention, most pairing it with semaglutide as CagriSema, and none includes retatrutide. FDA's position is blunt: "Retatrutide and cagrilintide cannot be used in compounding under federal law." The blends sold online, and how the two compare, are on retatrutide and cagrilintide.

Growth hormone peptides and TRT for muscle

These are the muscle stacks. They share one problem: each moves a number retatrutide also moves, sometimes in the opposite direction.

Tesamorelin

Of the growth hormone peptides in the table, tesamorelin is the only one with an FDA approval, and it's narrow: reducing excess belly fat in adults with HIV and lipodystrophy. The Egrifta WR label says it's "not indicated for weight loss management as it has a weight neutral effect." It also raised blood sugar: 5% of people on it reached an A1C of 6.5% or higher by week 26, against 1% on placebo, while retatrutide cut A1C by 2.0 points on 9 mg in TRANSCEND-T2D-1 and by 2.2 points on both doses in TRANSCEND-T2D-2 (efficacy estimand in both). Belly fat is the reason most people look at it; what retatrutide alone does there is on retatrutide and belly fat. See retatrutide and tesamorelin.

CJC-1295 and ipamorelin

Neither is approved. FDA's compounding risk page lists serious adverse events with CJC-1295, "including increased heart rate and systemic vasodilatory reaction," and cites a published study with serious events, including a death, when ipamorelin was given into a vein for gut motility. Ipamorelin is still in FDA's category 2 for outsourcing facilities. Retatrutide raises heart rate too: in the Phase 2 obesity trial, heart rate rose with dose and peaked at week 24. Sermorelin and HGH are covered with these on retatrutide with growth hormone peptides.

Testosterone (TRT)

Testosterone is a prescription drug, and FDA says it's "approved solely for use in men who lack or have low testosterone levels in conjunction with an associated medical condition." In February 2025, FDA said blood pressure monitoring studies had confirmed a rise in blood pressure with all testosterone products. Retatrutide went the other way, lowering systolic pressure by up to 12.3 mmHg in TRIUMPH-1 (efficacy estimand, Lilly's ADA release). In TRIUMPH-2, reported in September 2026 and published in The Lancet, 12 mg cut it by 10.8 mmHg in people with obesity and type 2 diabetes (efficacy estimand, Lilly's release). So one drug can hide the other's effect on a home reading. Details on retatrutide with TRT.

Skin, energy and recovery peptides

This group has the least human data of all.

GHK-Cu

People add it for loose skin and hair shedding during fast weight loss. FDA says injected GHK-Cu may carry a risk of immune reactions and that "there are limited data in humans." Lilly's releases and the journal abstracts give no hair loss rate for retatrutide, as of October 2026 (more on retatrutide hair loss); for tirzepatide, the Zepbound label lists hair loss in 4% to 5% of people, against 1% on placebo. The GLOW and KLOW blends are unpacked on retatrutide and GHK-Cu.

MOTS-c

FDA says it "has not identified any human exposure data on drug products containing MOTs-C administered via any route." The first registered Phase 2a trial started on February 2, 2026 in China: about 120 adults with prediabetes and overweight, measuring insulin sensitivity at 12 weeks, with primary completion estimated for February 2027. See retatrutide and MOTS-c.

BPC-157 and TB-500, the wolverine stack

This pair is sold for injuries and gut repair. FDA says it has "no, or only limited, safety-related information" for BPC-157 and hasn't found any human exposure data for TB-500. ClinicalTrials.gov now lists a Phase 2 BPC-157 hamstring trial (about 120 people) and a Phase 1/2 TB-500 heart biomarker trial (about 80), both started in February 2026 in China. The same company, Hudson Biotech, sponsors both, plus the MOTS-c trial and the one retatrutide listing that isn't Lilly's. None tests GLP-1 side effects, and none has results.

NAD+

Nobody has studied NAD+ with retatrutide. We searched ClinicalTrials.gov and found no trial pairing it with any GLP-1 drug, and no data on how the two interact. Supplements people do ask about on retatrutide, like electrolytes and fiber, are covered on supplements with retatrutide.

AOD-9604

AOD-9604 is a modified fragment of human growth hormone, and it's banned in sport by the World Anti-Doping Agency, according to a 2015 paper in Drug Testing and Analysis. It has no record on ClinicalTrials.gov, and FDA's page notes serious adverse events that "may be associated with AOD-9604, though causality is not clear."

Our read: "AOD-9604 vs retatrutide" isn't a close call on evidence. One has an 80-week Phase 3 trial with a 28.3% average weight loss on 12 mg (efficacy estimand; 25.0% regardless of adherence); the other has no registered trial we could find.

Two vials, two sets of unknowns

Every add-on outside a prescription comes from the same unregulated market as the retatrutide. That market already has a record. In its June 19, 2026 alert, Victoria's health department linked 6 cases of acute liver injury since January 2026 to products labeled Retatrutide, possibly from a contaminant, and the TGA's test found a vial with no retatrutide in it at all.

A stack adds a second problem. If your liver tests go up or a rash appears, you can't tell which vial did it. If you're comparing sellers who list retatrutide for sale, the only real check on what's inside is a batch-specific third-party test whose batch number matches your vial, and a stack means doing that check twice. What to look for in a seller is on the retatrutide vendors page.

Before you add anything to retatrutide

Our read: most stacks aim at a side effect or a worry, and a doctor can often treat the problem itself with something that has data behind it. If you go ahead anyway:

• Tell every prescriber you have, including a TRT or diabetes doctor, that you're on retatrutide. The known interactions are on retatrutide drug interactions.
• Add one thing at a time, weeks apart, so you can tell what caused a change. Retatrutide's half-life is about 6 days (per a 2024 Nature Medicine paper), so a dose is still working when the next one arrives; there's more on retatrutide half-life.
• Take extra care with insulin or a sulfonylurea. In the Zepbound label's diabetes trial, low blood sugar hit 10.3% of people taking tirzepatide with a sulfonylurea, against 2.1% on tirzepatide without one. That's tirzepatide data, but retatrutide lowers blood sugar too.
• Keep a record of batch numbers for every vial, in case a regulator or doctor asks.
• Count alcohol as an add-on. What's known is on retatrutide and alcohol, and doses for retatrutide alone are on the retatrutide dosage page.

If you want retatrutide without the guesswork, the legal routes as of October 2026 are Lilly's trials and its expanded access program. The registry entry is for adults with a BMI of 35 or higher and at least 2 serious obesity-related complications who haven't done well on the highest dose of an approved weight-loss drug and can't join a trial, and the treating doctor, not you, contacts Lilly. The steps are on how to get retatrutide.