GLP-1 medications like semaglutide (Ozempic, Wegovy) and tirzepatide (Zepbound, Mounjaro) are the most effective weight-loss drugs we’ve ever had, and for some people they also lower heart attack risk. They’re not for everyone. The real decision is about medical risk, muscle preservation, cost, and whether you can stay on the drug long enough for it to matter.
How well do they actually work?
The numbers are large. Semaglutide takes off about 15 percent of body weight over roughly 68 weeks (the STEP trials, NEJM 2021),1 and tirzepatide reaches about 21 percent at the top dose (SURMOUNT-1, NEJM 2022).2 Head to head, tirzepatide won, around 20 percent versus 14 percent.3 That’s weight loss only bariatric surgery used to reach. And it’s not just the scale: in people with existing heart disease and excess weight, semaglutide cut major cardiovascular events, heart attack, stroke, and cardiovascular death by 20 percent over about four years (SELECT, NEJM 2023, roughly 17,600 people), no matter how much weight they actually lost.4
Who benefits most, and who should wait?
The clearest candidates are adults with a BMI of 30 or higher, or 27 and up with a weight-related condition like type 2 diabetes, high blood pressure, sleep apnea, or heart disease. That’s the FDA-approved group, and the 2026 American College of Physicians guideline now puts these drugs first-line.5 The single strongest case is someone who already has heart disease and carries extra weight, because that’s where the 20 percent reduction in major cardiovascular events was proven.4 If your blood sugar is also drifting up, they do double duty, lowering glucose and weight at once;6 I get into reading that number in the A1C piece.
Who should wait or skip: if your BMI is under 27 and you’re otherwise healthy, there’s no trial behind it and no approval. Anyone with a personal or family history of medullary thyroid cancer shouldn’t take them at all.7 And if you can’t commit to the long haul, read the tradeoff below before you start.
How to protect muscle while losing weight
When you lose weight quickly, some of it is muscle, not just fat. On GLP-1s, roughly a quarter to 40 percent of the weight you lose is lean mass (closer to 35 percent in semaglutide studies, 25 percent with tirzepatide).8 That proportion is actually about what you’d lose with any rapid weight loss; it just adds up to a lot here because the total loss is so big. The protection comes from the plan around the drug. In pooled data, lifting weights dropped the muscle share of weight loss to about 18 percent, versus roughly 30 percent on the drug alone.8 Aim for protein in the range of 1.2 to 1.6 grams per kilogram a day and strength-train two or three times a week.9 This matters most for adults over 65, who have the least muscle to spare.10 And protein by itself isn’t enough; you have to actually train.9
The stopping tradeoff: weight regain and cost
Stop the drug and the weight mostly comes back. When semaglutide was withdrawn in the STEP-1 extension, people regained about two-thirds of what they’d lost within a year, and the blood pressure and metabolic gains faded along with it.11 Tirzepatide looked the same.12 Worse, the regained weight is disproportionately fat, so stopping can leave your body composition in a worse spot than where you started.12 Treat these like blood-pressure medicine, not a cleanse: they work while you take them. We also don’t yet have multi-decade safety data at these doses.7 Cost is a separate barrier: list prices run roughly $1,000 to $1,350 a month, and weight-loss coverage is often limited (Medicare will not cover obesity alone).13 One more thing: compounded versions are cheaper but aren’t FDA-reviewed, have caused documented dosing errors, and every major society advises against them.14
Start only with a muscle and long-term plan
If your BMI is 30 or higher, or 27-plus with something like diabetes, high blood pressure, or sleep apnea, these are worth a real conversation, and the case is strongest if you already have heart disease. Go in with three things settled: a plan to strength-train and hit your protein so you hold onto muscle, a budget for the long haul because stopping usually means regaining, and realistic expectations about nausea during the dose ramp-up.7 If your BMI is under 27 and you’re healthy, this isn’t your tool yet. And if you’re over 65, ask specifically about protecting muscle before you start. The drug does the easy part. Keeping the result is the actual work.