GLP-1 without the hype

GLP-1 medications for weight loss work, and the trials are not subtle: semaglutide moved about 15% of body weight and tirzepatide moved more. But they are tools, not shortcuts. The weight returns when the medication stops, some of what you lose is muscle unless you plan for it, and the version you take and the clinician behind it decide the result.

Key takeaways

• In trials, semaglutide (Wegovy) produced ~15% weight loss; tirzepatide (Zepbound) reached ~20%+ and beat semaglutide head-to-head.
• Stop the drug and most of the weight comes back — about two-thirds within a year in the semaglutide extension study.
• Roughly a quarter to 40% of the weight lost can be muscle, so resistance training and protein are part of the plan, not optional.
• Branded GLP-1s are FDA-approved and consistently dosed; compounded versions are now tightly restricted and carry extra risk.
• A GLP-1 belongs inside clinician-guided care with baseline labs, not a one-click refill.

What is a GLP-1, and what does it actually do?

A GLP-1 receptor agonist copies a gut hormone your body releases after eating. It slows how fast the stomach empties, quiets appetite signaling in the brain, and helps you feel full on less. That is the mechanism the marketing skips: these drugs act on hunger and satiety, not willpower.

Two molecules lead the category. Semaglutide is sold as Ozempic (approved for type 2 diabetes) and Wegovy (approved for weight management). Tirzepatide, sold as Mounjaro and Zepbound, adds a second gut hormone called GIP, which is part of why it tends to outperform. OPTMZ is independent of the manufacturers; the subject here is the evidence, not a brand.

Semaglutide vs tirzepatide: how much weight do people actually lose?

A lot in the trials, with the caveat that a trial average is not a promise for any one person.

In the STEP 1 trial, adults with obesity on semaglutide 2.4 mg lost about 15% of body weight over 68 weeks, versus 2–3% on placebo. Tirzepatide raised the ceiling in SURMOUNT-1, and when the two were compared directly in the 2025 SURMOUNT-5 trial, tirzepatide produced close to 50% more weight loss and a larger drop in waist circumference (18.4 cm vs 13.0 cm). Individual results vary widely with dose, tolerance, and whether the plan includes nutrition and training. That variation is where a clinician reviewing your labs earns their place.

What happens if you stop taking a GLP-1?

The weight returns. In the STEP 1 extension study, people who came off semaglutide regained about two-thirds of what they had lost within a year, roughly 11.6 percentage points of body weight over 52 weeks, even with continued lifestyle support. The improvements in blood pressure and lipids faded alongside it.

The honest read: for most people a GLP-1 is ongoing care for a chronic condition, not a 12-week course you graduate from. A program that sells it as a quick cycle is selling the hype, not the medicine.

Do GLP-1s cause muscle loss?

Some of the weight you lose quickly is lean tissue. Across recent GLP-1 studies, lean soft tissue accounted for roughly 26% to 40% of total weight lost. And weight regained after stopping comes back mostly as fat, which can leave your body composition worse than where you started.

This is manageable, and it is why the plan matters as much as the prescription. Resistance training several days a week and adequate protein (research-informed targets land near 1.6 to 2.0 g/kg of body weight per day) preserve muscle while fat comes off. A GLP-1 without a strength-and-protein plan is half a program.

Who should not take a GLP-1?

A GLP-1 is not right for everyone, and this is a clinician's decision after evaluation. It is contraindicated for people with a personal or family history of medullary thyroid carcinoma or MEN 2. It calls for caution with a history of pancreatitis, gallbladder disease, or certain GI conditions, and it is not a treatment for type 1 diabetes or used in pregnancy. The common side effects are gastrointestinal (nausea, vomiting, diarrhea, constipation), usually worst early and eased by slow dose titration.

None of that argues against the category. It is why treatment starts with an evaluation and labs, not a checkout button.

Compounded vs branded GLP-1: the version that isn't in the ads

Branded GLP-1s (Wegovy, Zepbound, Ozempic, Mounjaro) are FDA-approved, made to a consistent dose, and studied in the trials above. Compounded semaglutide and tirzepatide surged while the branded drugs were in shortage, but those shortages have resolved (tirzepatide in October 2024, semaglutide in February 2025), and the FDA has been closing the pathways that allowed large-scale compounding, proposing in April 2026 to remove these drugs from the 503B outsourcing bulks list. The FDA has also logged hundreds of adverse-event reports tied to compounded versions, many from dosing errors with multi-dose vials.

A narrow, legitimate role remains for patient-specific compounding through a 503A pharmacy when a clinical need cannot be met by the commercial product, such as a documented allergy to an inactive ingredient. At OPTMZ, branded GLP-1s are the public offering; a compounded alternative is discussed privately with your clinician only when clinically appropriate, never as a discount hero. If price is the only reason a program steers you toward compounded, treat that as a flag.

What good GLP-1 care looks like

A GLP-1 program worth your time starts with a baseline: an evaluation and metabolic labs (HbA1c, lipids, and more) so the clinician knows what they are treating. It titrates the dose deliberately to manage side effects, pairs the medication with a muscle-preserving nutrition and training plan, and rechecks your labs on a schedule instead of auto-refilling into silence. That is the line between a prescription and actual care, and it decides whether the results last. See how OPTMZ structures this in the Weight loss program.

OPTMZ's branded GLP-1 offering is Zepbound® (tirzepatide), via LillyDirect — see the Weight program.

Educational content, medically reviewed. Not a substitute for individual medical care; treatment decisions require a clinician evaluation.

Medications are issued only when clinically appropriate after provider evaluation. OPTMZ Health connects patients with independent licensed providers and does not itself practice medicine or dispense medication.

Sources

• Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022. dom-pubs.onlinelibrary.wiley.com
• SURMOUNT-5: Tirzepatide versus Semaglutide for the Treatment of Obesity. New England Journal of Medicine, 2025. nejm.org
• U.S. FDA. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. fda.gov
• Preservation of lean soft tissue during weight loss induced by GLP-1 and GLP-1/GIP receptor agonists. PMC, 2025. pmc.ncbi.nlm.nih.gov