Weight Management

The weight management conversation got rewritten in the last three years and most people still haven’t caught up. The drugs that did the rewriting are GLP-1 agonists. Semaglutide, sold as Ozempic for diabetes and Wegovy for weight loss. Tirzepatide, sold as Mounjaro and Zepbound. They’re the biggest shift in obesity medicine since bariatric surgery, and unlike most things that show up in clinic with that kind of hype, they actually work.

That comes with some asterisks. A guy who’s been carrying 60 extra pounds for a decade can lose 35 of them on a once-weekly injection without spending his life hungry. The drug isn’t fixing the underlying setup, though. And the compounded “semaglutide” some telehealth clinic is shipping from a strip-mall pharmacy in Florida isn’t the molecule that was studied in the STEP trials. It’s something adjacent.

The two issues nobody likes to talk about are muscle loss and the discontinuation rebound. The rebound is the big one. If you don’t have a plan for what happens when you stop, you’re not really planning your weight loss. You’re renting it.

How the molecule does what it does

GLP-1 stands for glucagon-like peptide-1. Your gut already makes it. It’s part of the signaling system that tells your brain you’ve eaten enough and tells your pancreas to release insulin when glucose shows up. The drugs are synthetic versions of that hormone, modified so they last a week in your bloodstream instead of a few minutes.

Three things happen when you inject one. Your stomach empties slower, so food sits there longer and you feel full on smaller portions. Your appetite signaling in the hypothalamus gets dampened, so the constant background hum of “I could eat” gets quieter. And glucose handling improves, which is why these drugs were diabetes meds first and weight loss meds second. The hunger reduction is the part patients describe most. People tell me food just stopped being interesting. The mental real estate that used to be occupied by what’s for lunch goes quiet. For someone who’s spent thirty years thinking about food more than they wanted to, that quiet is the whole point.

Tirzepatide adds a second receptor (GIP) and tends to outperform semaglutide in head-to-head data. Roughly 15-20% body weight loss on tirzepatide versus 12-15% on semaglutide in the trials, though individual results vary a lot.

Who’s actually a candidate

FDA labeling is BMI 30+, or BMI 27+ with a weight-related comorbidity like hypertension, sleep apnea, or type 2 diabetes. Insurance draws tighter lines. The practical question I ask is whether the patient has tried to lose weight through behavior alone, what got in the way, and whether their metabolic picture justifies a long-term medication.

A patient came in last winter who’d been on three different weight-loss programs in the last six years. Mid-thirties, BMI 34, prediabetic, sleep apnea machine collecting dust under the bed because he hated wearing it. What he kept coming back to wasn’t a dramatic story. It was the same quiet thing. He’d lose twenty pounds, hit a stretch where work got hard or his daughter got sick or both, and the weight would come back over the next year and then some. He’d done that loop three times. He came in tired of doing it. We started semaglutide, got him lifting twice a week with a trainer because he wouldn’t do it on his own, and at the fifteen-month mark he’s lost 42 pounds. The CPAP is still under the bed but he doesn’t need it anymore, which is its own problem.

The patients I’m more cautious with are the ones at BMI 28 with no metabolic flags who want to drop 15 pounds for aesthetic reasons. The drug will probably work for them. The question is whether they’re signing up for a medication they’ll be on indefinitely to maintain a result behavior could plausibly handle. Most haven’t thought about that part yet.

The compounded gray market

This part is a mess. When demand for Ozempic and Wegovy outstripped supply in 2022 and 2023, the FDA allowed compounding pharmacies to produce semaglutide. Telehealth clinics flooded in. You can get “semaglutide” shipped to your door for a fraction of branded pricing.

Compounded semaglutide isn’t FDA-approved semaglutide. The active ingredient may be a different salt form (semaglutide sodium, semaglutide acetate) that was never studied for safety or efficacy in humans. Sterility varies pharmacy to pharmacy. Some patients are underdosed. Some are overdosed and end up in the ER with intractable vomiting. As the shortage status changes, the legal basis for a lot of these compounded products is going away.

If your “semaglutide” costs $200 a month and arrives in an unlabeled vial from a pharmacy you’ve never heard of, you’re not on the drug from the trials. You’re on something adjacent to it.

Compounded medications fill real gaps and I’m not going to pretend the practice itself is suspect. The GLP-1 compounding space has attracted operators who aren’t careful and patients who don’t know what questions to ask. If you’re going to use one, verify the pharmacy is licensed, ask what form of the active ingredient they’re using, and have someone clinical actually following you, not a 90-second video intake from a kid in a polo shirt.

Side effects, muscle loss, and the part nobody warns you about

The GI side effects get all the attention. Nausea is the big one, especially in the first few weeks and after every dose increase. Vomiting in a smaller percentage. Constipation is constant for some people. Most of it fades. A subset of patients can’t tolerate the drug at any dose. The titration schedule exists for a reason and rushing it is how people end up miserable.

Less common but real: gallstones (significant rapid weight loss does this regardless of mechanism, and GLP-1s accelerate gallstone formation specifically), pancreatitis (rare but the signal is real, particularly if you’ve had it before), and a theoretical thyroid C-cell tumor risk that came from rat studies and hasn’t shown up in human data but lives on the label.

The muscle loss issue is the one most patients don’t hear about until they’ve already lost the muscle. Any significant weight loss, GLP-1 or otherwise, takes lean mass along with fat. Without resistance training and adequate protein (call it 1.2 to 1.6 grams per kilogram body weight), you end up smaller but metabolically worse off. Slower resting metabolism, weaker grip strength, harder to maintain the loss. I tell every patient starting one of these drugs that they’re signing up for a strength program too. Two sessions a week, compound movements, progressive overload. Non-negotiable if I’m prescribing.

The discontinuation rebound is the part the marketing won’t mention. When you stop semaglutide, gastric emptying speeds back up, appetite signaling returns, and hunger comes back with interest. The STEP-4 trial found patients who stopped regained about two-thirds of their lost weight inside a year. Before you start, you need to be honest about whether you’re prepared to take this medication for years, possibly indefinitely, and what your off-ramp looks like if cost or insurance changes.

Using the runway for something durable

GLP-1s are a powerful tool that work best when they’re propping up real behavior change. The patients who do best are the ones who use the appetite quieting as breathing room to build the habits they couldn’t build before. Strength training. Protein-forward eating. Sleep that isn’t garbage. Walking most days. The boring stuff that nobody can sell you.

The drug buys you a runway. What you do with the runway is the whole game. The patients who treat semaglutide like a magic shot and don’t change anything else lose the weight and then watch it come back when life forces them off the medication, and life will eventually force most of them off. The patients who use the year of quiet appetite to wire in habits that survive the drug end up somewhere they can actually live. The molecule is doing the same work in both groups. The year is the part that gets used differently.