Retatrutide vs Zepbound: Weight Loss, Sleep Apnea and Price Compared

Zepbound is Lilly's brand of tirzepatide, a different drug from retatrutide. It has been approved in the US for weight since November 2023 and for obstructive sleep apnea since December 2024, while retatrutide is still in Phase 3 trials with no approved version. On weight, the gap in retatrutide vs Zepbound is real but smaller than the headlines. Counting everyone who started treatment, retatrutide 12 mg averaged 25.0% weight loss over 80 weeks in TRIUMPH-1, and Zepbound 15 mg averaged 20.9% over 72 weeks on its label. As of October 2026, Zepbound self-pay starts at $299 a month. Retatrutide has no price, because there's nothing approved to sell.

This page compares retatrutide with Zepbound as a product you can actually fill a prescription for, label and price included. For the molecule-level comparison, including how the two drugs' doses and receptors differ, see retatrutide vs tirzepatide. Mounjaro is the same tirzepatide sold for type 2 diabetes: retatrutide vs Mounjaro.

Retatrutide vs Zepbound at a glance

Every Zepbound figure below comes from its FDA label (revised August 2026), the FDA's approval notices or Lilly's own price pages. The retatrutide figures come from the TRIUMPH-1 paper in NEJM, the TRIUMPH-2 paper in The Lancet and Lilly's TRIUMPH releases.

The two diabetes figures now use the same counting method, but they still come from different trials of different lengths. Lilly's July release led with the other method, as if everyone stayed on treatment, which gave 20.8% for TRIUMPH-2.

Weight loss on Zepbound's label and in TRIUMPH

Zepbound's label reports the result for everyone who was randomized, including people who stopped their shots (the treatment-regimen estimand). In SURMOUNT-1, 2,539 adults without diabetes lost 15.0% on 5 mg, 19.5% on 10 mg and 20.9% on 15 mg over 72 weeks, against 3.1% on placebo.

TRIUMPH-1 reported the same kind of number for retatrutide over 80 weeks, and it's the primary result in the NEJM paper: 17.6% on 4 mg, 23.7% on 9 mg and 25.0% on 12 mg, against 3.9% on placebo. So retatrutide's lowest Phase 3 dose sits between Zepbound 5 mg and 10 mg, and its 9 mg dose already beats Zepbound's top dose. The TRIUMPH-1 group was also heavier at the start, averaging 112.7 kg with a BMI of 40.0, against 104.8 kg and 38.0 in SURMOUNT-1.

The numbers you'll see in most headlines come from the other method. Lilly's retatrutide releases lead with the efficacy estimand, which asks what happens if everyone stays on treatment:

That's where the widely shared 28.3% comes from, and it isn't the NEJM headline. Putting it next to Zepbound's 20.9% makes the gap look like 7.4 points when the fair gap is about 4. The full walk-through of the two methods, with SURMOUNT-2 and TRIUMPH-2 for people with diabetes, sits on our retatrutide vs tirzepatide page, and every trial result is on the retatrutide weight loss results page. To see what those averages mean at your own starting weight, try the weight loss calculator.

Sleep apnea is approved for Zepbound and still in trials for retatrutide

The FDA approved Zepbound on December 20, 2024 for moderate to severe obstructive sleep apnea in adults with obesity, based on two 52-week trials in people without diabetes. The label counts moderate as 15 to 30 breathing pauses or shallow breaths per hour of sleep (the apnea-hypopnea index, or AHI) and severe as 30 or more.

Retatrutide's data comes from a sleep apnea substudy inside TRIUMPH-1. Until October that was one "up to" number from Lilly; the NEJM paper of October 21, 2026 now gives every dose and a placebo group. The table uses NEJM's main method for retatrutide (the hybrid-treatment estimand) and the label's numbers for Zepbound.

The label's percentages look odd next to its own numbers (5.3 an hour on a 50.1 baseline isn't 3%) because the label analyzes percent change as its own measure, so they don't divide out of the columns beside them. Lilly's June "up to 36.1 an hour (60.6%)" is an efficacy-estimand number, which is why it reads higher than anything in the table.

Our read: once placebo is subtracted, retatrutide's sleep apnea result (24.4 and 21.9 an hour on the two higher doses) sits next to Zepbound's (20 and 23.8), not far above it. Retatrutide's group started more severe and was treated for 80 weeks instead of 52, and nobody has compared the two directly.

People with type 2 diabetes did similarly in TRIUMPH-2-OSA (448 people, baseline 55.9 an hour): down 19.2, 24.7 and 25.4 an hour on 4, 9 and 12 mg against 10.3 on placebo. Zepbound's label trials didn't cover that group. Back in the no-diabetes trials, the averages on treatment still sat in the moderate range, by our arithmetic: about 24.3 an hour on retatrutide 9 mg (58.6 minus 34.3) and about 27.6 in Zepbound's Study 5 (52.9 minus 25.3).

Side effects and dropouts

Both drugs cause mostly stomach side effects, and both bunch them up in the weeks after a dose increase. Retatrutide's top dose causes more of them. On Zepbound 15 mg, the label reports nausea in 28% of people against 8% on placebo. On retatrutide 12 mg in TRIUMPH-1, nausea hit 42.4% against 14.8%, which is about 4 in 10 people. Dropouts follow the same pattern: about 1 in 9 people on retatrutide 12 mg (11.3%) stopped because of side effects, against about 1 in 15 on Zepbound 15 mg (6.7%), with placebo rates of 4.9% and 3.4%.

One side effect sets retatrutide apart. Burning or oversensitive skin (dysesthesia) affected 12.5% of people on 12 mg in TRIUMPH-1, against 0.4% on Zepbound 15 mg. Lilly says most cases were mild to moderate and most resolved during treatment. The table of every common side effect is on our tirzepatide comparison; retatrutide side effects and nausea cover the rest.

What Zepbound costs, and what retatrutide costs

Zepbound's self-pay prices on LillyDirect, re-checked October 31, 2026 and unchanged since September 27, are the same for vials and the KwikPen: $299 a month for the 2.5 mg starting dose, $399 for 5 mg and $449 for 7.5 mg to 15 mg if you refill within 45 days. Miss that window and the price goes to $499 for 7.5 mg or $699 for 10 mg to 15 mg. Needles or syringes cost extra.

Here's what 12 fills cost at those prices, using the label's fastest schedule of one step up every 4 weeks:

The on-time price is flat from 7.5 mg up, so reaching 15 mg costs the same as stopping at 7.5 mg. Late refills are what move the bill. Lilly counts a month as 28 days (one KwikPen of 4 weekly doses), so 12 fills cover 48 weeks. A full 52 weeks takes a 13th fill, another $449 at 7.5 mg or above.

With coverage, the numbers drop. Lilly's savings page lists single-dose pens for as little as $25 a fill if your commercial plan covers Zepbound, under a card whose terms end December 31, 2026. On Medicare Part D, the Medicare GLP-1 Bridge program covers the KwikPen for $50 a month with prior authorization from July 2026 to December 2027, though it excludes people with type 2 diabetes, moderate to severe sleep apnea or fatty liver disease.

Retatrutide has no price. Lilly's October FAQ says that after the trials and FDA review it plans to make sure retatrutide is "priced to reflect the overall value to the healthcare system", and its July release says retatrutide "cannot be legally sold or marketed for human use" (is retatrutide legal has the detail). Vials labeled as retatrutide are still sold online, and none of them is Lilly's product. In a safety alert published September 14, 2026, Australia's TGA reported that one it tested contained no retatrutide at all, only semaglutide at about 8 times the level in approved products. If you're weighing online listings of retatrutide for sale, that page covers what they are and how people read batch test reports, and our retatrutide price page dates what sellers ask.

Moving from Zepbound to retatrutide

No trial has tested switching people from Zepbound to retatrutide, and there's no dose conversion between them. Zepbound's label says it isn't recommended alongside other tirzepatide products or any GLP-1 receptor agonist, and retatrutide acts on the GLP-1 receptor.

The legal routes to retatrutide right now are a clinical trial or Lilly's expanded access program. That program is narrow: adults with a BMI of 35 or more despite the highest available dose of an approved weight drug, plus 2 or more serious obesity-related conditions, and the request has to come from your doctor. Our guide to switching from tirzepatide covers the timing questions in more detail.

Is retatrutide better than Zepbound?

On average weight loss, yes: retatrutide 9 mg and 12 mg beat Zepbound 15 mg in separate trials, by about 3 to 4 points on matching math. On everything else a real decision rests on, Zepbound leads. It's approved for weight and sleep apnea, its price is public, and its top dose caused less nausea (28% against 42.4%) and fewer dropouts (6.7% against 11.3%).

Our read: if Zepbound is working for you, the published numbers don't give a strong reason to leave an approved drug for one that isn't approved. The open question is people who have stalled on Zepbound 15 mg, and no retatrutide trial has published results for that group.

Questions worth taking to your doctor:

• Am I still losing weight on my current Zepbound dose, or have I leveled off for several months?
• Would a higher dose help, and would my plan or LillyDirect price it differently?
• If sleep apnea is part of why I'm treated, is my AHI being rechecked?
• Would I qualify for a retatrutide trial listed on ClinicalTrials.gov?

Retatrutide has been tested head-to-head once, and not against tirzepatide. In TRANSCEND-T2D-2, reported October 28, 2026, adults with type 2 diabetes lost 19.5% (9 mg) and 20.9% (12 mg) of their weight over 80 weeks against 9.4% on Ozempic 2 mg, on the efficacy estimand. That speaks to semaglutide, not Zepbound. The comparison with tirzepatide is TRIUMPH-5, which pits retatrutide against tirzepatide in about 800 adults with obesity and measures weight change at week 80. ClinicalTrials.gov lists its estimated primary completion as November 2026, and no topline has been released.

Approval timing is unsettled. 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. For how retatrutide compares with other drugs, start with is retatrutide a GLP-1.