The fat-loss peptides Kinobody is promoting

Greg O'Gallagher's current education product, The Ripped Artiste, teaches lean men how to use tirzepatide (Zepbound, Mounjaro) and to a lesser extent retatrutide (Eli Lilly's still-unapproved triple agonist) for a leaner physique.¹ He runs a companion telehealth service, Kino Clinic, that connects members to physicians who will prescribe.

His framing is sophisticated. He acknowledges that men running these drugs alone "are getting skinny not chiseled,"¹ and he sells his training system as the part that fills the muscle back in. He recommends tirzepatide over retatrutide for lean users on the grounds that the lean-to-fat ratio of weight lost is more favorable, the FDA has already approved tirzepatide for obesity, and the heart rate increase is smaller.²

If you're lean and considering this, the useful question is whether the published data supports running these drugs in a body already near its fat minimum. This post walks through what the data says.

What these drugs do

Tirzepatide is a dual agonist at the GLP-1 and GIP receptors. Retatrutide adds a third receptor, glucagon. Both work primarily by suppressing appetite and slowing gastric emptying. The result is a calorie deficit you barely notice. People on tirzepatide eat less without the willpower tax that usually comes with losing fat.

The deficit is large. In SURMOUNT-1, the trial that got tirzepatide approved for obesity, the 15 mg arm lost about 20% of body weight over 72 weeks.³ Retatrutide's TRIUMPH-4 data from December 2025 produced 28.7% loss at 68 weeks, the largest weight loss recorded in any obesity trial.⁴

These aren't subtle drugs.

The side effects in the trial population

The published side-effect profile is class-typical. Most of it shows up regardless of which GLP-1-class drug you run.

Gastrointestinal. Roughly 80% of the 15 mg tirzepatide arm in SURMOUNT-1 reported at least one of nausea, diarrhea, vomiting, or constipation. Severity peaks during dose titration and is dose-dependent.³ For retatrutide, vomiting at the 12 mg dose was nearly nine times the placebo rate, and a third of users discontinued for tolerability reasons.⁵

Thyroid C-cell tumors. Tirzepatide and semaglutide both carry a boxed warning. In rats, both drugs produced dose-dependent C-cell adenomas and carcinomas. Whether this signal applies to humans is unknown. The drugs are contraindicated in patients with personal or family history of medullary thyroid carcinoma or MEN2 syndrome.³⁶

Pancreatitis. Acute pancreatitis, including fatal cases, has been observed across the class. The signal is small, and it isn't zero.³

Gallbladder disease. Cholelithiasis and cholecystitis appeared in the trials at meaningful rates. Rapid weight loss is a known driver, and these drugs produce rapid weight loss.³

Cardiovascular. Mean heart rate increased 2.1 to 5.4 bpm in SURMOUNT-1, dose-dependent. Retatrutide's increases are larger. Ambulatory blood pressure dropped, which is good.⁷

Suicidality signal. The FDA reviewed and removed the warning label after concluding there was no causal signal.⁸ One pharmacovigilance analysis still found a reporting odds ratio of 1.45, with a higher signal in patients also on antidepressants.⁹ It's worth knowing if you have any relevant history.

These are the risks measured in the population the trials were designed to study, adults with a BMI of 27 or higher.

The lean-mass problem

This is the part that matters most for the audience Kinobody is selling to.

Across major trials, a meaningful fraction of total weight lost is lean mass:

• Tirzepatide 15 mg in SURMOUNT-1: about 25% of weight lost is lean mass.¹⁰
• Semaglutide in STEP-1: about 39 to 45% of weight lost is lean mass.¹⁰
• Retatrutide: roughly 30 to 35% lean-mass loss.¹¹

A 25% lean-mass fraction sounds tolerable. For an obese person it usually is, because the absolute amount of fat lost is so large that the lean-to-fat ratio of the body improves. For someone already lean, the math inverts.

Take a 175 lb lifter at 14% body fat. They carry roughly 24 lb of fat and 151 lb of lean mass. They run tirzepatide and lose 12 lb. At the SURMOUNT-1 ratio, that's 9 lb of fat and 3 lb of lean mass. They're now 163 lb at just under 10% body fat, and they've lost 3 lb of lean tissue.

That's a lot of lean mass to give up. It isn't all muscle, but a meaningful share of it is. The visible result is the "skinny not chiseled" look Kinobody himself describes. His training system is positioned as the answer to that. No published study tests whether resistance training plus tirzepatide preserves lean mass at parity with resistance training plus a normal calorie deficit. The implicit claim is that it does. The data doesn't exist yet.

As Peter Attia puts it, "The potential benefits of fat loss among healthy-weight individuals are minimal and are unlikely to offset the sizable health risks associated with reduced lean mass."¹²

The rebound problem

Weight regain after stopping these drugs is well documented.¹³ SURMOUNT-4 followed tirzepatide users after they stopped and saw over half the lost weight return within 52 weeks.¹⁴ STEP-10 saw the same pattern with semaglutide, with 40% of weight regained within 28 weeks. By 18 months off the drug, average weight is back to baseline.¹³

The catch is what gets regained. Across the rebound literature, the tissue that returns is preferentially fat, not lean mass.¹⁵ So a lean user runs a 12-week tirzepatide course, loses 3 lb of lean mass and 9 lb of fat, then stops. Six months later they've regained 7 lb, and most of that 7 lb is fat. They end up with less muscle and roughly the same body fat percentage they started with. Net body composition gets worse.

If the drug is run indefinitely, the rebound is avoided. The lean-mass loss isn't.

Retatrutide specifically

Retatrutide isn't approved by the FDA. Eli Lilly has late-stage trial data,⁴ and as of September 2026 it hasn't filed the new drug application. In July the company said it would submit in the first quarter of 2027, after gathering more manufacturing and quality-control data.¹⁶ Any retatrutide a consumer can buy today is compounded or grey-market. There's no authorized compounding pathway for it.

Tirzepatide is different. It's FDA approved for obesity (as Zepbound) and for type 2 diabetes (as Mounjaro). A licensed prescriber writing for a patient who meets the BMI criteria is operating inside the indicated population. A lean fitness audience, by definition, isn't.

The compounded GLP-1 market that drove most fitness-audience use is also closing. The FDA declared the semaglutide shortage resolved in February 2025 and set enforcement deadlines through April and May 2025.¹⁷ The era of the cheap compounded vial bought through a telehealth funnel is mostly over. What remains is either the brand drug at brand pricing or the grey market with no quality control.

What Kinobody acknowledges and what he leaves out

He acknowledges the lean-mass problem. He prefers tirzepatide over retatrutide for lean users on that basis. He notes the heart rate difference. He recommends physician supervision through Kino Clinic.

When we reviewed his public content in May 2026, it didn't mention the rebound literature, the thyroid C-cell warning, the pancreatitis signal, the compounded-market enforcement actions, or whether his audience falls inside any drug's approved indication. The Ripped Artiste also referenced a "GLP and Peptide Education Guide" without naming what's in the broader peptide stack on its public marketing pages. BPC-157 is classified as an unapproved drug. The FDA has flagged it as a significant safety risk for compounding pharmacies, and it's prohibited for athletes by USADA and the DoD.¹⁸ AOD-9604 failed its late-stage trial. 5-amino-1MQ has zero published human trials. Whether any of these are in the guide isn't visible from the public materials.

The decision the data supports

Tirzepatide was trialed and approved for people with obesity. That's the population the evidence covers, and in that population the weight loss is real while the drug is running. This post is written for someone who's already lean.

At Leanos, we do not use these drugs and do not recommend taking them to build a lean physique. Everything above is the reason.

If you're already lean and considering it for a leaner physique, the published data doesn't support running it. You'd be pulling lean mass out of a body that doesn't have much to spare. You'd be signing up for a drug you'll eventually stop, and the tissue that comes back is fat. You'd be paying for and injecting a prescription drug for a goal it wasn't approved or trialed to address.

A normal calorie deficit produced by walking, eating mostly protein and produce, and doing the lifts you already know how to do doesn't cause vomiting, doesn't require a prescription, doesn't carry a boxed warning, and produces a body composition you keep. That's the trade nobody is selling on Instagram.

If you decide to do it anyway, do it on the brand drug, with a real physician, with baseline DXA and labs, and with a plan for what happens when you stop. Don't run retatrutide before it's approved. Don't stack it with peptides whose human safety database has a sample size in the dozens.

We'll keep watching the trial pipeline and update this post if the picture changes.

Footnotes

1. Kinobody. The Ripped Artiste. Product page. https://rippedartiste.com/ ↩ ↩²

2. O'Gallagher, G. Tirzepatide vs Retatrutide: My Honest Take. Kinobody blog, 2025. https://kinobody.info/tirzepatide-vs-retatrutide-my-honest-take/ ↩

3. U.S. Food and Drug Administration. Zepbound (tirzepatide) Prescribing Information, 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/218316Orig1s000lbl.pdf ↩ ↩² ↩³ ↩⁴ ↩⁵

4. Drugs.com. Retatrutide regulatory history (TRIUMPH-4 results, December 2025). https://www.drugs.com/history/retatrutide.html ↩ ↩²

5. Efficacy and safety of retatrutide: a systematic review and meta-analysis. PMC, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12026077/ ↩

6. U.S. Food and Drug Administration. Wegovy (semaglutide) Prescribing Information, 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s024lbl.pdf ↩

7. Effects of tirzepatide on ambulatory blood pressure and heart rate. AHA Hypertension, SURMOUNT-1 substudy. https://www.ahajournals.org/doi/10.1161/HYPERTENSIONAHA.123.22022 ↩

8. U.S. Food and Drug Administration. Drug Safety Communication: removal of suicidal behavior and ideation warning on GLP-1 receptor agonists. https://www.fda.gov/drugs/drug-safety-communications/fda-requests-removal-suicidal-behavior-and-ideation-warning-glucagon-peptide-1-receptor-agonist-glp ↩

9. Association of GLP-1 receptor agonists with suicidal ideation: meta-analysis of FAERS data. PMC, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC11823376/ ↩

10. Neeland IJ, et al. Changes in lean body mass with glucagon-like peptide-1-based therapies. Diabetes, Obesity and Metabolism, 2024. https://pubmed.ncbi.nlm.nih.gov/38937282/ ↩ ↩²

11. GLP-1 receptor agonists induce loss of lean mass: so does caloric restriction. PMC review, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12322565/ ↩

12. Attia, P. The downside of GLP-1 receptor agonists. peterattiamd.com. https://peterattiamd.com/the-downside-of-glp-1-receptor-agonists/ ↩

13. Weight regain after liraglutide, semaglutide, or tirzepatide interruption: a narrative review. PubMed, 2025. https://pubmed.ncbi.nlm.nih.gov/40507553/ ↩ ↩²

14. TCTMD. Weight regained within 18 months of stopping GLP-1 drugs (SURMOUNT-4 reporting). https://www.tctmd.com/news/weight-regained-within-18-months-stopping-glp-1-drugs ↩

15. Rebound or retention: meta-analysis of weight regain after GLP-1 discontinuation. PMC, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12535773/ ↩

16. BioPharma Dive. Lilly, with new data, to seek FDA approval of obesity drug retatrutide, July 2026. https://www.biopharmadive.com/news/lilly-retatrutide-fda-application-obesity-drug-results/825987/ ↩

17. U.S. Food and Drug Administration. FDA clarifies policies for compounders as the national GLP-1 supply begins to stabilize, 2025. https://www.fda.gov/drugs/drug-alerts-and-statements/fda-clarifies-policies-compounders-national-glp-1-supply-begins-stabilize ↩

18. Operation Supplement Safety / U.S. Department of Defense. BPC-157: Prohibited Peptide and Unapproved Drug Found in Health and Wellness Products. https://www.opss.org/article/bpc-157-prohibited-peptide-and-unapproved-drug-found-health-and-wellness-products ↩