# Semaglutide: A GLP-1 Peptide That Reaches the Brain's Appetite Circuits > Semaglutide is an FDA-approved GLP-1 peptide that quiets appetite at its source — the brain. A forward-looking, plain-English digest of the mechanism and the trials, every claim cited. A forward-looking, plain-English read of how a once-weekly GLP-1 peptide reaches the hypothalamus and brainstem to turn down hunger, with every number sourced to the trial that measured it. ## Start here Semaglutide is a medicine your body already knows how to read. It is a lab-built copy of GLP-1, a hormone your gut releases after a meal that tells your brain you have had enough. The natural version is gone in about two minutes; this engineered version lasts roughly a week, so one weekly dose keeps the signal switched on. The headline story is the brain. In studies, semaglutide reaches appetite-control regions deep in the brain and turns down hunger — many people describe their constant "food noise" going quiet. It is approved by the U.S. Food and Drug Administration (FDA) for type 2 diabetes, for long-term weight management, to lower the risk of heart attack and stroke in certain people, and (in 2025) for a serious fatty-liver disease. What to watch for matters too. The most common downside is an upset stomach, especially when the dose is first raised. What people actually report — the good and the bad — is on [the effects page](/effects). ## What is semaglutide Semaglutide is a 31-amino-acid peptide — a short protein chain — that copies about 94% of human GLP-1 (glucagon-like peptide-1), the gut hormone that boosts insulin and curbs appetite after eating [4]. Two small edits to the chain are what make it a once-weekly drug instead of a two-minute one. A swap at position 8 (to an unusual building block called Aib) blocks the enzyme DPP-4, which normally chews up GLP-1 within minutes. A fatty-acid tail clips onto the chain and grabs onto albumin, the most abundant protein in blood, so the kidneys clear the drug slowly [13]. The payoff of that chemistry is a long, steady signal. Semaglutide's half-life — the time for blood levels to fall by half — is about one week, so it takes roughly five weeks to fully clear after the last dose [13]. That is the structural reason a single weekly injection, or a single daily tablet, can keep appetite circuits engaged around the clock. ## Semaglutide peptide: the numbers that define it As a peptide drug, semaglutide has a precise molecular identity worth stating plainly. Its formula is C187H291N45O59 and its molecular weight is about 4,114 daltons — large for a drug, small for a protein. Its CAS registry number is 910463-68-2 and its ATC drug-class code is A10BJ06. What sets this semaglutide peptide apart from the natural hormone is engineered durability. Native GLP-1 is destroyed almost instantly; the redesigned molecule resists that breakdown and binds albumin so tightly that it circulates for about a week [4][13]. The result is a peptide that behaves less like a fleeting gut signal and more like a steady background instruction to eat less — which is exactly how the brain studies describe its effect [4]. ## What the trials have actually shown The evidence base here is unusually large. In the STEP 1 trial of adults with overweight or obesity, once-weekly semaglutide 2.4 mg produced a mean body-weight change of -14.9% at 68 weeks, versus -2.4% on placebo [1]. In SELECT, a 17,604-person trial of adults with heart disease and obesity but no diabetes, the drug cut major cardiovascular events — heart attack, stroke, or cardiovascular death — by 20% (HR 0.80) [3]. In FLOW, it lowered serious kidney-disease events in type 2 diabetes with chronic kidney disease by 24% (HR 0.76) [6]. Those are human results, not animal extrapolations. But the *why* behind them traces back to the brain: rodent work shows semaglutide reaching the brainstem and hypothalamus to cut food intake without slowing metabolism [4]. To go deeper, start with [semaglutide mechanism of action](/mechanism-of-action), then read [how does semaglutide work](/how-it-works), or jump straight to the [Semaglutide research](/research). ## How to read this site This is an editorial digest, not a clinic and not a store. It summarizes published, peer-reviewed research and approved-label information about semaglutide in plain language. It does not recommend a dose for any individual and it is not medical advice. Doses appear here only as they were studied or labeled, described in the third person — never as instructions for you. Where a number appears, a citation follows. The full source list, with DOIs and PubMed links, lives on the [Semaglutide references](/references) page. The most human page — what people report feeling, including the downsides — is the [Semaglutide effects](/effects) page, and it leads the navigation for a reason. --- A forward-looking digest that decodes the semaglutide literature — mechanism first, every figure traced to the trial that measured it.