# Semaglutide: What the Trial Record Actually Shows > Semaglutide is an FDA-approved GLP-1 receptor agonist. A plain-English, fully cited reading of the trial record — and how it compares with tirzepatide in the SURMOUNT-5 head-to-head. A documentation-grade, plain-English digest of the published evidence: every trial number pinned to the study that produced it, and the head-to-head against tirzepatide read fairly. ## The short version Semaglutide is a medicine you take once a week as a shot, or once a day as a pill, that copies a natural gut hormone called GLP-1 (a signal your body releases after eating that tells you you are full and helps control blood sugar). It is FDA-approved, meaning regulators reviewed large human trials and cleared it — for type 2 diabetes, for long-term weight management, to lower the risk of heart attack and stroke in certain people, and, since 2025, for a serious fatty-liver disease. In a large weight-loss trial, people lost about 15% of their body weight over roughly 16 months [1]. It also has real downsides — nausea is common early on, and weight tends to come back if you stop [1][17]. The honest comparison against a newer drug, tirzepatide, and what people actually report — including the rough parts — is on [the effects page](/effects). Nothing here is medical advice or a dose to follow. ## What the semaglutide literature has demonstrated Semaglutide is a long-acting agonist of the GLP-1 receptor — a synthetic copy of the incretin hormone GLP-1 (glucagon-like peptide-1), engineered so it lasts about a week in the body instead of a couple of minutes [11]. That single change in durability is what turned a fragile gut hormone into a once-weekly medicine, and the trial record built on it is one of the largest in modern metabolic medicine. The headline weight number comes from STEP 1: once-weekly subcutaneous semaglutide 2.4 mg produced a mean body-weight change of -14.9% from baseline to week 68, versus -2.4% with placebo, in adults with overweight or obesity and no diabetes [1]. In type 2 diabetes, the SUSTAIN program established HbA1c (a three-month average blood-sugar marker) lowering across doses [9]. The protection runs deeper than the scale. In SELECT (n=17,604), in people with established cardiovascular disease and obesity but no diabetes, semaglutide cut major adverse cardiovascular events by 20% versus placebo (HR 0.80; 95% CI 0.72-0.90) [3]. In FLOW (n=3,533), it reduced major kidney-disease events by 24% in type 2 diabetes with chronic kidney disease [6]. This is the [Semaglutide research](/research) record in one paragraph: weight, glucose, heart, kidney. ## How it works, in one read The weight effect is mostly in the brain, not the gut. Rodent work mapped semaglutide reaching the brainstem and the hypothalamic arcuate nucleus — the small region that runs hunger and fullness — where it switches up the "I'm full" neurons and switches down the "I'm hungry" neurons, lowering food intake without dropping the body's energy burn [4]. People describe the result as the "food noise" going quiet. It also does the classic incretin jobs: it nudges the pancreas to release insulin only when blood sugar is high, calms the hormone that raises blood sugar, and slows how fast the stomach empties [5]. That last one is why nausea shows up — and why it usually fades. The full mechanism, with citations, is on [the research page](/research). ## How semaglutide compares with tirzepatide The question readers ask most is whether the newer drug wins. The fairest answer is a single head-to-head trial. In SURMOUNT-5 (n=751), a direct comparison in adults with obesity, tirzepatide produced greater mean weight loss than semaglutide at 72 weeks: -20.2% versus -13.7%, a roughly 6.5-percentage-point advantage that was statistically significant (P<0.001) [7]. In diabetes, SURPASS-2 pointed the same direction for HbA1c and weight [8]. That does not make semaglutide a runner-up. It carries the larger cardiovascular-outcomes evidence base to date (SELECT) [3] and a kidney-outcomes trial (FLOW) [6], and it is the one with both a pill and a shot. The full side-by-side, with the numbers in a table, is the point of this site — read [semaglutide vs tirzepatide](/vs-tirzepatide). ## What to watch for An honest digest names the downsides plainly. The dominant adverse effects are gastrointestinal — nausea, vomiting, diarrhea, constipation — mostly mild-to-moderate and concentrated during the dose-escalation period [13]. Nausea affects roughly a third of patients in the safety literature [5]. Stopping the drug is followed by substantial weight regain — a mean of about 11.6 percentage points within a year in the STEP 1 extension — which is why obesity is framed as a chronic, not a curable, condition [17]. There are also things to flag and not overstate: a boxed warning for medullary thyroid carcinoma carried over from rodent studies (no clear human signal) [14], and reports of hair shedding that track rapid weight loss rather than the drug itself [18]. All of it, including what people report from real use, lives on [the effects page](/effects). --- A documentation-grade reading room for the semaglutide trial record, read side by side with tirzepatide — every figure traced to the study that measured it; not a clinic, not a prescriber, and nothing here dosed, compounded, or sold.