Semaglutide vs Tirzepatide vs Retatrutide: three generations of weight-loss drugs

Patients ask me to compare semaglutide vs tirzepatide vs retatrutide: which is strongest, and whether it’s worth waiting for the newest one. By weight lost, semaglutide takes off the least, tirzepatide more, and retatrutide the most. That order follows the pharmacology. Each drug acts on one more gut-hormone receptor than the one before, and more receptors means more weight lost. Whether the strongest drug is the right one for you is a different question, and often the answer is no.

How each drug works

The drugs differ by how many gut hormones they mimic.

Semaglutide acts on a single receptor, GLP-1. It curbs appetite and slows stomach emptying, and it’s the active drug in Ozempic and Wegovy. In the STEP 1 trial, it cut body weight by about 14.9% over 68 weeks.

These drugs may do more than shift weight. There’s early evidence they cut drinking too, which I break down in GLP-1 and alcohol.

Tirzepatide acts on two receptors, GLP-1 and GIP. In SURMOUNT-1, the 15 mg dose reached about 20.9% over 72 weeks, a clear step up from semaglutide.

Retatrutide acts on three, adding glucagon to the pair. The glucagon receptor raises energy expenditure instead of only suppressing appetite, and the weight loss reflects it: about 24.2% at 48 weeks in its phase 2 trial, and 28.3% over 80 weeks in Eli Lilly’s phase 3 TRIUMPH-1 result. It isn’t approved, and I don’t prescribe it.

Semaglutide vs Tirzepatide vs Retatrutide, side by side

A table makes the pattern easy to see. Treat it as a rough guide. The trials ran for different lengths, enrolled different patients, and reported averages under research conditions with close follow-up. Real-world weight loss usually comes in lower, because side effects, cost, and missed doses all pull against the trial numbers.

Drug	Receptors	Brand names	FDA status for obesity	Average weight loss in trials
Semaglutide	GLP-1 (1)	Ozempic, Wegovy	Approved (Wegovy)	~15% at 68 weeks
Tirzepatide	GLP-1 + GIP (2)	Mounjaro, Zepbound	Approved (Zepbound)	~21% at 72 weeks
Retatrutide	GLP-1 + GIP + glucagon (3)	None yet	Investigational, not approved	~24% at 48 weeks (phase 2)

One number the table hides is how many people reach a given target. In the retatrutide phase 2 trial, 83% of the people on the 12 mg dose lost at least 15% of their body weight, against 2% on placebo. That’s about 8 of every 10 people hitting that mark. The average loss on that dose was around 24% of body weight, which for a 250-pound person is roughly 60 pounds. Effect sizes this large are rare in medicine, and they’re part of why these drugs have changed obesity treatment.

Stronger drugs bring more side effects

The same dose escalation that drives more weight loss also drives more nausea, vomiting, diarrhea, and constipation. Across these trials, gastrointestinal side effects were the most common reason people felt unwell or stopped. They tend to be worst as the dose climbs and ease with time, which is why every one of these drugs starts low and increases slowly.

Retatrutide’s phase 2 trial also showed a dose-dependent rise in heart rate that peaked around 24 weeks. That is the kind of signal a longer, larger trial has to sort out before a drug reaches the market. A medication with several years of post-approval data behind it sits on firmer ground than one resting on a single phase 2 study.

Cost and access decide as much as biology. Insurance coverage for weight-loss drugs is inconsistent, the branded versions run several hundred dollars a month without it, and supply has been unreliable. A drug you can’t get or afford steadily is worse than a slightly less powerful one you can take without interruption. Stopping and restarting tends to bring the weight back and the side effects forward.

What these drugs do in the brain

These are gut hormones, but their receptors also sit in the brain, in the circuits that govern appetite and reward. That placement is why the drugs blunt hunger, and it’s why they interest me as a psychiatrist.

The reward effect reaches past food. In a 2025 randomized trial, semaglutide reduced alcohol craving and drinking in adults with alcohol use disorder. Many patients also describe a drop in “food noise,” the constant background pull toward eating. A drug that quiets that signal is acting on motivation and reward. I’ve written more about how GLP-1 drugs affect mood and motivation, and about whether the weight loss itself can lift depression.

Early case reports raised a worry about suicidal thoughts on GLP-1 drugs. The FDA reviewed those reports and, in January 2024, said its evaluation found no evidence that these medicines cause suicidal thoughts or actions, and it later asked manufacturers to remove the warning language. I still ask about mood at every visit, because rapid weight change and shifting appetite can affect how a person feels, and because I’m the one managing it.

The muscle question

When weight comes off fast, some of what you lose is muscle. In a DXA substudy of SURMOUNT-1, about 75% of the weight lost on tirzepatide was fat and about 25% was lean tissue. Reviews of semaglutide show a similar pattern, with lean-mass loss running anywhere from near zero to about 40% of the total depending on the study.

Some lean-mass loss comes with any large weight reduction, including from dieting alone. It matters most for older adults, who have less muscle to spare, and for anyone already frail. Two things protect muscle during treatment: enough protein, roughly 1.2 to 1.6 grams per kilogram of body weight a day, and resistance training a few times a week. I raise both before a patient starts.

Matching the drug to the patient

The right drug depends on the person.

For many patients, semaglutide is the sensible start. It has the longest track record, the most prescribing experience behind it, and enough weight loss for most goals.

Tirzepatide makes sense when semaglutide hasn’t done enough, when there’s a large amount of weight to lose, or when type 2 diabetes is also present. Its two-receptor action helps blood sugar as well as weight.

Beyond the drug itself, several things move the decision: heart disease, kidney function, other medications, cost, and how much nausea someone can tolerate. Two people at the same weight can land on different drugs for good reasons.

Where retatrutide stands

Retatrutide is the most powerful of the three in trials and the least available in practice. As of July 2026 it is investigational. Eli Lilly has reported strong phase 3 results, but the drug has not been approved by the FDA, and there is no legal pathway to a compounded or online version.

If you see retatrutide sold online, it’s a gray-market product with no oversight of dose, purity, or sterility. I don’t prescribe it, and I’d advise against buying it. When it’s approved and I can prescribe it safely, that will change. Until then, an approved drug you can take consistently beats a stronger one you can’t obtain legally.

How I choose with patients in North Carolina

I run a cash-pay telehealth psychiatry practice in North Carolina, and medical weight management is part of it. One physician handles the whole picture: the drug, the dose, the side effects, the mood, and the metabolic markers that shift as the weight changes. Weight, metabolism, and mood move together, and I treat them that way. If you’re in North Carolina and want that kind of oversight, you can book a free consultation.

I start most patients on an approved GLP-1, escalate slowly, watch tolerability, and track more than the scale: energy, mood, muscle, blood pressure, and labs. Whether a psychiatrist is the right prescriber for this is a fair question, and I’ve answered it in detail elsewhere. The short version is that these drugs act on the brain as much as the gut, and managing that is what I do.

Frequently asked questions

Which of these is most effective for weight loss?

In trials, retatrutide produced the most weight loss, then tirzepatide, then semaglutide. For a specific person, the best drug is the one they can tolerate, afford, and take consistently, which is often not the strongest on paper.

Is tirzepatide better than semaglutide?

Tirzepatide produced more weight loss in trials and adds a blood-sugar benefit through its second receptor. It also tends to cost more and has a shorter track record. Which one is better depends on your goals, whether you have diabetes, and how well you tolerate it.

Should I wait for retatrutide?

As of July 2026 retatrutide is not approved, so waiting means going untreated in the meantime. If you have a medical reason to lose weight now, an approved drug you can start today is usually the better call. There is no legal compounded version to bridge the gap.

Do these drugs cause muscle loss?

Some of the weight lost is lean tissue, about a quarter of it in the SURMOUNT-1 body-composition substudy. Adequate protein and resistance training reduce that loss. It matters most for older adults and anyone already low on muscle.

Are they safe if I have depression?

The FDA’s review found no evidence that GLP-1 drugs cause suicidal thoughts or actions, and the warning language was later removed. I still monitor mood throughout treatment, because big shifts in appetite and weight can change how a person feels.

This article is for education and does not replace individual medical advice. Retatrutide is investigational and not FDA-approved as of July 2026. Medication decisions depend on your full history and should be made with your prescriber. If you are having thoughts of suicide or self-harm, call or text 988 to reach the Suicide and Crisis Lifeline.

References

1. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PMID 33567185.
2. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PMID 35658024.
3. Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. PMID 37366315.
4. Eli Lilly and Company. Retatrutide (TRIUMPH-1) phase 3 topline results. Company press release, June 2026.
5. Look M, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study. Diabetes Obes Metab. 2025;27(5):2720-2729. PMID 39996356.
6. Bikou A, et al. A systematic review of the effect of semaglutide on lean mass. Expert Opin Pharmacother. 2024;25(5):611-619. PMID 38629387.
7. Hendershot CS, et al. Once-Weekly Semaglutide in Adults with Alcohol Use Disorder. JAMA Psychiatry. 2025;82(4). PMID 39937469.
8. U.S. Food and Drug Administration. Update on FDA’s ongoing evaluation of reports of suicidal thoughts or actions in patients taking GLP-1 receptor agonists. FDA Drug Safety Communication, January 2024.