Semaglutide is the most-searched peptide there is, and the compound that put the entire GLP-1 weight loss category on the map. It is the established name, the one with the longest real-world track record, and the reference point every newer compound gets measured against. Here is the full breakdown: what it is, how it works, the actual FDA dose schedule, what the trials showed, and the honest picture on side effects and what happens when people stop.

What is semaglutide?

Semaglutide is a GLP-1 receptor agonist given as a once-weekly subcutaneous injection. It is sold as Wegovy for weight management and as Ozempic for type 2 diabetes (the same molecule, different indication-specific dosing). It works on a single hormonal pathway, GLP-1, which is the distinction that matters when comparing it to the dual- and triple-agonist compounds that came after it. It has a half-life of about seven days, which is what makes once-weekly dosing practical.

How it works

GLP-1 is a naturally occurring incretin hormone the gut releases when food arrives. It signals the pancreas to produce insulin, suppresses glucagon, slows gastric emptying, and communicates satiety to the brain. Semaglutide mimics that hormone, and the practical result is reduced appetite and increased fullness, plus slower stomach emptying, so the main effect a person feels is eating less without fighting cravings all day. It is fundamentally an appetite and satiety tool with metabolic effects on insulin and glucose, not a metabolism-accelerator.

The evidence

Semaglutide has the deepest evidence base of any modern weight loss peptide. The pivotal trial, STEP 1, published in the New England Journal of Medicine in 2021, enrolled nearly 2,000 adults with obesity (or overweight with a weight-related condition, excluding diabetes) and reported an average weight loss of about 14.9% at the 2.4 mg maintenance dose over 68 weeks. Later trials reinforced the picture: a head-to-head against the previous-generation GLP-1 liraglutide showed semaglutide producing roughly 15.8% versus 6.4%, establishing it as the stronger GLP-1 monotherapy before tirzepatide arrived. That long, large, well-published record plus years of real-world use is exactly why semaglutide is the established, best-understood option in the category, even though it is no longer the strongest on raw weight loss numbers.

Dosing

Semaglutide for weight management follows a deliberate, slow dose-escalation schedule, and the slow ramp is the point, it is designed to minimize gastrointestinal side effects by letting the body adapt.

The starting dose is intentionally low, 0.25 mg once weekly for the first four weeks, then it titrates upward roughly every four weeks to the 2.4 mg weekly maintenance dose, reaching maintenance over about 16 weeks. The 2.4 mg dose is the FDA-approved weight-management target and the dose that produced the STEP 1 results. The prescribing information notes that if the 2.4 mg dose is not tolerated, it can be temporarily reduced to 1.7 mg. A newer higher-dose option (Wegovy HD, 7.2 mg) has since been introduced, narrowing one of tirzepatide's advantages, though long-term outcome data at that dose is thinner so far. For the diabetes indication (Ozempic), the dose targets are lower, generally 1.0 to 2.0 mg.

Timeline

Appetite suppression tends to show up within the first one to two weeks, but meaningful weight loss accumulates over months. The month-by-month pattern from the trials is steep early loss that slows into a plateau after about month 12. The headline 14.9% figure is a 68-week result, so it is the product of more than a year on the full maintenance dose, not a fast outcome.

Side effects

The side-effect profile is dominated by gastrointestinal effects: nausea, constipation, and related GI complaints, worst during the dose-escalation phase, which is exactly why the titration is slow. For most people these ease as the body adapts. The slow ramp and the option to hold or temporarily reduce a dose are the main tools for managing tolerability.

The regain question

One of the most important and least-discussed findings from the STEP program concerns what happens after stopping. In the STEP 1 extension and STEP 4, after participants discontinued semaglutide, they regained about two-thirds of the weight they had lost within a year, and the cardiometabolic improvements (blood pressure, glucose, lipids) drifted back toward baseline. This is not a sign the drug failed or stopped working; it reflects how obesity behaves as a chronic condition, and the biology of regain is well understood. It is a genuinely important thing to understand going in: the results are tied to continued use.

Where it fits

Semaglutide is the established, best-documented option in the GLP-1 class, the one with the longest safety record and the most real-world use. It is the reasonable choice for someone who values a proven, well-understood compound over the strongest possible number, and it remains highly effective even though tirzepatide and retatrutide post higher trial figures. Its main practical caveat is the regain pattern after stopping, which frames it, like the rest of the class, as a long-term tool rather than a short course.