Semaglutide research, plotted study by study.

Before the details

Here is the whole semaglutide research story in one breath. Your gut makes a hormone called GLP-1 after meals; it tells the pancreas to release insulin, slows the stomach, and signals fullness to the brain. The natural version is gone in two minutes. Semaglutide is a redesigned, long-lasting copy that does the same jobs for about a week per dose. Scientists then ran some of the largest trials in metabolic medicine to see what that does. The answer, repeated across studies: substantial weight loss ^[1], fewer heart attacks and strokes in high-risk people ^[3], slower kidney decline in diabetes ^[6], and better blood sugar ^[2]. A brand-new head-to-head found a related drug, tirzepatide, edged it out on weight ^[7]. The rest of this page walks through each of those findings and the brain biology underneath them, in plain language.

How does semaglutide work

Semaglutide works by impersonating GLP-1 at its receptor — but for far longer. Native GLP-1 is chopped up within about two minutes by the enzyme DPP-4. Semaglutide's position-8 swap to a non-natural amino acid (Aib) blocks that cut, and its C18 fatty-acid tail clips onto albumin, the blood's main carrier protein, hiding the peptide from kidney clearance and stretching its half-life to roughly a week ^[20].

Once active, it pulls three levers. It boosts insulin release from the pancreas, but only when blood sugar is high (a glucose-dependent effect, which is why it rarely causes lows on its own). It suppresses glucagon, the hormone that raises blood sugar. And it slows gastric emptying, so food leaves the stomach more gradually.

The weight effect, though, is mostly central. Rodent studies traced labeled semaglutide into the brainstem and the hypothalamic arcuate nucleus — the brain's appetite hub — where it activates the POMC/CART neurons that signal satiety and silences the NPY/AgRP neurons that drive hunger, lowering food intake and shifting food preference without reducing energy expenditure ^[4]. Earlier work in mice had already shown the arcuate nucleus is required for this class of drug to drive weight loss, establishing the circuit semaglutide later plugged into ^[12].

The weight-management trials (STEP)

The STEP program is the backbone of the obesity evidence. In STEP 1, 1,961 adults with overweight or obesity and no diabetes took once-weekly 2.4 mg semaglutide or placebo for 68 weeks; the mean body-weight change was -14.9% versus -2.4% ^[1]. STEP 5 extended the question to two years and found the weight loss was sustained and still well ahead of placebo over 104 weeks ^[8].

Durability cuts both ways. STEP 4 used a withdrawal design: everyone took semaglutide for a 20-week run-in, then half switched to placebo. Those who stayed on it kept losing (a further -7.9%), while those who switched regained (+6.9%) ^[9]. The STEP 1 extension quantified the rebound after stopping entirely — a mean regain of about 11.6 percentage points within a year ^[17]. And the drug is not adults-only in the data: in STEP TEENS, adolescents with obesity had a significantly greater BMI reduction on 2.4 mg than on placebo over 68 weeks ^[10]. The companion STEP 2 report, published in a separate journal, covered weight management in adults who also had type 2 diabetes ^[11].

Beyond the scale: heart and kidney outcomes

The outcome trials are why semaglutide is more than a weight drug. SUSTAIN-6 randomized 3,297 people with type 2 diabetes at cardiovascular risk and found the composite of cardiovascular death, nonfatal heart attack and nonfatal stroke fell with semaglutide (HR 0.74; 95% CI 0.58-0.95) — though complications of pre-existing diabetic retinopathy were more frequent (HR 1.76) ^[2]. SELECT took the question into obesity without diabetes: 17,604 adults with established cardiovascular disease, where 2.4 mg cut major adverse cardiovascular events by 20% (HR 0.80; 95% CI 0.72-0.90) ^[3].

FLOW carried the protection to the kidneys. In 3,533 people with type 2 diabetes and chronic kidney disease, once-weekly 1.0 mg semaglutide reduced major kidney events — kidney failure, a 50% or greater drop in filtration rate, or kidney/cardiovascular death — by 24% (HR 0.76; 95% CI 0.66-0.88) ^[6]. A dedicated safety review frames the overall risk/benefit as favorable, with transient gastrointestinal effects dominating the adverse-event profile ^[5].

Semaglutide vs tirzepatide

The most-asked comparison now has a direct answer. In SURMOUNT-5, a head-to-head trial of 751 adults with obesity, the dual GIP/GLP-1 agonist 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].

The honest reading is nuanced. Tirzepatide hits two receptors (GIP and GLP-1) where semaglutide hits one, and on this weight endpoint it won. But semaglutide carries the larger and longer cardiovascular- and kidney-outcomes record to date — SELECT, SUSTAIN-6 and FLOW have no exact tirzepatide equivalent yet. "Which is better" depends entirely on which outcome you are asking about, and both are GLP-1-pathway successes rather than rivals in a zero-sum race.

Compounded semaglutide

Compounded semaglutide is semaglutide prepared by a compounding pharmacy rather than the approved, manufactured product. During the federally declared shortage of roughly 2022 to early 2025, compounding was permitted to fill supply gaps. The published and regulatory record flagged real problems: documented dosing errors, adverse events requiring hospitalization, and products containing unverified or non-pharmaceutical active ingredients. After the shortage was declared resolved in early 2025, those compounding pathways were curtailed, leaving ongoing regulatory and telehealth uncertainty. The key point for a reader: compounded or non-pharmaceutical sources fall outside the approved-product evidence base that every trial on this site studied — the STEP, SUSTAIN, SELECT and FLOW numbers describe the manufactured product, not a compounded substitute.