Zepbound is an FDA-approved medicine you can get with a prescription. As of August 2026, according to Thrive Wellness Institute, FDA had not approved retatrutide for any use. Both are studied as weekly injections, but retatrutide adds a third target, and its strongest results so far are Lilly’s own announcements that have not yet been fully peer reviewed.
What is retatrutide, and how is it different from Zepbound?
Zepbound is the brand name of tirzepatide. Tirzepatide works on two gut-hormone receptors, GIP and GLP-1. Retatrutide works on those same two plus a third, the glucagon receptor. Thrive Wellness Institute says the glucagon activity is intended to affect energy balance as well as appetite and blood sugar.
The GLP-1 part is shared by the whole drug class. The NAM Health Basics: GLP-1s page explains that these drugs slow stomach emptying, increase fullness and reduce appetite.
Retatrutide is also known by its research code, LY3437943. Tirzepatide carries the code LY3298176. Mounjaro and Zepbound are both tirzepatide. Mounjaro is approved for type 2 diabetes. Zepbound is approved for chronic weight management in eligible adults, and also for moderate-to-severe obstructive sleep apnea in adults with obesity. So if you are asking whether retatrutide beats Mounjaro, the answer depends on which brand and which use you mean. The two drugs have not been compared head to head.
Which one causes more weight loss?
The closest published comparison for Zepbound is SURMOUNT-5, which pitted tirzepatide against semaglutide, not retatrutide. Lilly’s retatrutide Phase 3 numbers come from its own topline announcement.
| Drug and dose | Trial | Length | Average weight change |
|---|---|---|---|
| Zepbound (tirzepatide) | SURMOUNT-5, adults with obesity or overweight plus a weight-related condition | 72 weeks | -20.2% (semaglutide 2.4 mg: -13.7%) |
| Retatrutide 12 mg | TRIUMPH-1 Phase 3, adults with obesity or overweight and no type 2 diabetes (Lilly topline) | 80 weeks | -25.0% (placebo: -3.9%) |
| Retatrutide 12 mg | Phase 2 obesity trial | 48 weeks | -24.2% |
These trials used different people, lengths and designs, so the rows are not a scorecard. The Phase 3 results are not from a trial against tirzepatide, which means nothing in this table proves one is better. The TRIUMPH-1 results have not yet been fully peer reviewed.
What are the side effects and risks of retatrutide?
In Lilly’s Phase 3 topline results, the most common problems were stomach and gut effects. Thrive Wellness Institute reports that these were generally mild to moderate. The same gut effects are common across GLP-1 medicines, according to Diabetes UK’s GLP-1 guide. If you are weighing Zepbound, read mounjaro side effects for a fuller breakdown of the tirzepatide profile.
| Side effect | What the reports say |
|---|---|
| Nausea, vomiting, diarrhea, constipation, decreased appetite | Common with retatrutide in the Phase 3 topline results, mostly mild to moderate |
| Dysesthesia (an abnormal sensation of tingling or numbness) | Reported more often than with placebo in some retatrutide groups |
| Urinary tract infections | Reported more often than with placebo in some retatrutide groups |
| Stopping because of side effects | Higher doses had higher discontinuation rates due to side effects in the reported trials |
| Warning signs that need urgent care | Yellowing of the skin or eyes, fever of 38C or more, tummy tenderness or swelling, fast heartbeat. Diabetes UK lists these for GLP-1 medicines. |
Diabetes UK says initial EMA and FDA investigations found no evidence that GLP-1 medicines cause suicidal thoughts or actions, but a small risk cannot be completely ruled out and monitoring continues. Contact your care team about any sudden mood change.
Thrive Wellness Institute also notes that these drugs do not selectively target muscle, but substantial weight loss can include some loss of lean tissue. Eating enough protein and resistance training are the usual ways people try to protect it. If hair loss worries you, bring it to your clinician along with the other side effects you are watching for.
Who can take retatrutide, and who can take Zepbound?
Zepbound eligibility generally involves obesity, or overweight plus a weight-related health condition, and a clinician decides whether it fits you. The medicine’s leaflet lists who should not use it, so read that with your clinician before you start.
Retatrutide has no approved prescribing guidance, so no one can be prescribed it yet. Its trials enrolled adults with obesity or overweight without type 2 diabetes (TRIUMPH-1), adults with type 2 diabetes (TRIUMPH-2), and adults with a BMI of at least 35 and established cardiovascular disease (TRIUMPH-3). Thrive Wellness Institute advises patients to avoid products marketed online as “research use” retatrutide.
How much does retatrutide cost, and can you get it now?
Retatrutide has no approved price. The FDA states that it has not been found safe and effective for any condition and cannot be used in compounding under federal law, according to Thrive Wellness Institute. The NAM Health Basics: GLP-1s page adds that the FDA has not assessed compounded GLP-1 formulations for safety, effectiveness or quality.
Prices and bundles change, so check the current Zepbound price directly with Lilly or your pharmacy. Ask your prescriber to explain the cost and any coverage before you start.
How fast does retatrutide start working?
Lilly’s Phase 3 results are reported at 80 weeks, and the Phase 2 results at 48 weeks. Long-acting GLP-1 drugs keep the receptor active across 24 hours, a difference that a PubMed Central review of GLP-1 receptor agonists explains alongside short-acting versions. Ask your clinician what to expect in the first weeks, since the reported results are at these later points.
What is not known yet about retatrutide?
- Approval: FDA has not approved retatrutide for any use.
- Peer review: The Phase 3 results are manufacturer announcements, and the full data are not yet fully peer reviewed.
- Head to head: The Phase 3 results are not a head-to-head trial against tirzepatide.
- Heart outcomes: TRIUMPH-3 was not designed or powered to prove a cardiovascular benefit.
- Top-end figures: A pre-specified extension subgroup of 532 people with a BMI of at least 35 reached up to 30% weight loss, but that is a selected group, not the full trial.
- Long-term safety: NAM reports that researchers continue to monitor muscle mass, bone health and mental well-being in people using GLP-1 drugs for longer periods.
Next steps and questions to ask a clinician
Zepbound is FDA-approved for chronic weight management in eligible adults; whether it or another approved medicine fits you is a decision for you and your clinician. Then read natural weight loss vs prescription medications to weigh a prescription against a routine you run yourself.
- Do I qualify for Zepbound based on my weight and health conditions?
- Which side effects should I watch for, and when should I call you?
- Given my health history, who should not use Zepbound?
- How do you manage nausea or vomiting if it starts?
- Is there a clinical trial for retatrutide that I could be eligible for?
- What is the plan if I stop, since appetite and weight can return?
By Gut, Gum and Nail Health Editorial Team
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.