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Bariatric (weight-loss) surgery still leads to more total weight loss than any medicine. Gastric bypass takes off about 25–30% of body weight, and a gastric sleeve takes off about 20–25%. Those losses hold for more than five years.
Brand-name semaglutide (Wegovy), at 14.9% in trials, still sits below a sleeve. But brand-name tirzepatide (Zepbound) at its top dose landed inside the sleeve’s range with no operation. People lost 20.9% by week 72 in SURMOUNT-1. Because the two now overlap, this decision belongs in a clinician’s office. A chart can’t make it for you.
Two different kinds of numbers
The drug numbers come from trials. STEP 1 (Wilding et al., NEJM 2021; 1,961 participants) randomly assigned people to brand-name semaglutide (Wegovy) 2.4 mg weekly or placebo. At week 68, the semaglutide group had lost 14.9% of their body weight on average, compared with 2.4% on placebo. SURMOUNT-1 (Jastreboff et al., NEJM 2022; 2,539 participants) did the same for brand-name tirzepatide (Zepbound). By week 72, people lost 15.0% on 5 mg, 19.5% on 10 mg, and 20.9% on 15 mg, compared with 3.1% on placebo.
The surgery numbers are a different kind of evidence. The 25–30% for bypass and 20–25% for the sleeve come from decades of registry data that track patients after surgery. They’re ranges that experts agree on, and they don’t come from randomized trials. No large trial has put surgery head-to-head against a modern GLP-1. So every comparison you’ll read, including this one, puts trial evidence on one side and tracking data on the other.
Still, bypass out-loses every drug on average. The matchup people search for most is semaglutide versus the gastric sleeve. The sleeve wins that one, because 14.9% sits below the 20–25% range. Tirzepatide at 15 mg versus the sleeve is the close call, since their ranges overlap.
Being able to stop cuts both ways
You can stop a weekly shot, and the trials that tested stopping show what that costs. In STEP 4 (Rubino et al., JAMA 2021), people who stopped brand-name semaglutide (Wegovy) at week 20 regained a lot of weight over the next year. Those who kept going kept losing.
SURMOUNT-4 (Aronne et al., JAMA 2024) is even clearer. After stopping brand-name tirzepatide (Zepbound), people regained about 14% of their body weight over the next year. Those who stayed on lost another 5.5%. The drug’s effect doesn’t linger. Appetite comes back as the drug leaves your body. So “you can stop” really means “you may need to take it with no end date.”
Surgery is the mirror image. A sleeve permanently removes most of the stomach, and a bypass reroutes the intestine around it. That permanence is the point, since your results don’t depend on a weekly choice to keep going. But it’s also the cost if your health or plans ever mean you need to undo it.
The risks don’t line up neatly
Surgery’s risks come mostly up front, from anesthesia and the operation itself. After that, you need vitamins, minerals, and regular checkups for life.
The drugs’ risks are spread out over time, and most come from the slowed stomach. That causes nausea, reflux, constipation, and early fullness, mostly while the dose is going up. The boxed warning is real but narrow. It concerns thyroid C-cell tumors in rodents. Whether that applies to humans is unknown. Anyone with a personal or family history of medullary thyroid carcinoma or MEN 2 is ruled out, and so is anyone who is pregnant.
The drugs also have one thing surgery doesn’t: a randomized trial of heart outcomes. SELECT (Lincoff et al., NEJM 2023) followed 17,604 people with heart disease and no diabetes for more than three years on average. Brand-name semaglutide (Wegovy) lowered major heart events by 20% in relative terms. It’s also the largest long-term safety study these drugs have. Surgery has decades of follow-up from tracking patients, but no randomized trial that big.
Who qualifies, and who decides
The usual cutoffs for GLP-1s are a BMI of 30 or more, or 27 or more with a weight-related condition. For surgery, guidelines have long drawn the line at a BMI of 40, or 35 with a condition like diabetes or sleep apnea. Newer guidance from surgeons’ groups argues for lower cutoffs. That leaves a wide overlap: a BMI of 36 with high blood pressure qualifies for both.
When you qualify for both, the deciding factors aren’t in any table. They include how bad your diabetes is, your history of reflux, plans for pregnancy, and what you’ve already tried. They also include how you weigh a permanent change to your body against taking medicine with no end date. You also don’t have to pick just one. GLP-1s are more and more often prescribed after surgery when weight comes back. But practice there is ahead of the research.
In the US, money is part of the decision. By law, regular Medicare Part D can’t cover drugs for weight loss, though a temporary Medicare program covers some brand-name GLP-1s for certain people through 2027. Many job-based plans leave them out too. Coverage for surgery is a separate question that depends on your plan. Check both before you assume anything. Zappy is cash-pay, and you can use FSA or HSA funds. Compounded semaglutide and tirzepatide are made by LegitScript-verified 503A US pharmacies. As compounded medicines, they are not FDA-approved. Current prices are on each treatment page.
Where to start
Make both options concrete instead of arguing about them in the abstract. For the medicine path, our GLP-1 guide covers how titration and the first months really go, and the five-minute quiz tells you whether you’d qualify. A clinician reviews every case within 24 hours.
If you might qualify for surgery, ask your primary care doctor whether a bariatric surgery consult makes sense at the same time. A surgeon who has examined you and a prescriber who has seen your labs will settle this better than any chart. Until someone runs the head-to-head trial, they’ll settle it better than the research can, too.
