Semaglutide

What it is

Semaglutide is a modified version of GLP-1, a 30-amino-acid gut hormone released after meals. Two amino acid changes protect it from the enzyme that destroys native GLP-1 within minutes, and a fatty acid chain lets it bind albumin in the blood, stretching its half-life to about a week. Novo Nordisk developed it as a successor to daily liraglutide. The oral forms pair the peptide with an absorption enhancer that lets enough survive the stomach to work. ¹⁷

The same molecule is sold at different doses under three brands. Ozempic and Rybelsus are for type 2 diabetes; Wegovy is the higher-dose version for weight management and now for cardiovascular risk reduction and liver disease. Demand has outrun supply at times, which fed a market in compounded semaglutide that the FDA has warned about repeatedly. ¹⁷¹⁵

How it works

Semaglutide activates GLP-1 receptors in several places at once. In the pancreas it increases insulin release when glucose is high and suppresses glucagon, which lowers blood sugar without causing hypoglycemia on its own. In the stomach it slows emptying, so meals feel filling for longer. In the brain it acts on appetite centers in the hypothalamus and brainstem to reduce hunger and food cravings, which is where most of the weight loss comes from. The cardiovascular benefit appears to be only partly explained by weight loss: in SELECT, an estimated third of the reduction in heart attacks and strokes was mediated through waist circumference reduction, and the benefit was present regardless of starting weight, suggesting direct effects on blood vessels and inflammation. ¹⁷¹¹

What human research shows

STEP 1 randomized 1,961 adults with obesity but no diabetes to weekly semaglutide or placebo for 68 weeks alongside lifestyle counseling. Mean weight loss was 14.9 percent versus 2.4 percent, and half of semaglutide patients lost at least 15 percent. In STEP 8, a head-to-head trial in 338 adults, semaglutide produced 15.8 percent weight loss versus 6.4 percent with daily liraglutide. STEP 4 showed what happens to people who stop: after 20 weeks on drug, those switched to placebo regained 6.9 percent over the next 48 weeks while those who continued lost a further 7.9 percent. In the STEP 1 extension, participants who stopped treatment regained two-thirds of their lost weight within a year. ²⁶⁸¹²

SELECT enrolled 17,604 adults aged 45 and older with cardiovascular disease and overweight or obesity but no diabetes. Over a mean of 40 months, the composite of cardiovascular death, heart attack or stroke occurred in 6.5 percent on semaglutide versus 8.0 percent on placebo, a 20 percent relative reduction. The benefit held in the quarter of participants with heart failure and across all baseline weights. FLOW, in people with type 2 diabetes and chronic kidney disease, showed a 24 percent reduction in kidney disease progression and cardiovascular death. ^39101113

In type 2 diabetes, SUSTAIN FORTE compared two semaglutide doses in 961 adults and found HbA1c reductions of 1.9 to 2.2 percentage points over 40 weeks. A 2023 meta-analysis of 17 trials in 14,940 patients found HbA1c reductions of about 1 to 1.4 points versus placebo. Against tirzepatide, a network meta-analysis of 28 trials found tirzepatide lowered HbA1c and weight more, and the SURMOUNT-1 tirzepatide trial reported up to 20.9 percent weight loss, above semaglutide's 15 percent, though the two have been compared directly only in diabetes. ⁴⁵¹⁶¹⁷

Safety

Nausea, diarrhea, vomiting and constipation are the common side effects, affecting a large share of users early in treatment and fading for most; in STEP 1, 4.5 percent stopped because of them, and in SELECT 16.6 percent discontinued for adverse events versus 8.2 percent on placebo. Gallbladder disease is more frequent, in part because rapid weight loss itself causes gallstones. The label carries a boxed warning about thyroid C-cell tumors seen in rodents, with no confirmed human signal, and contraindicates use in people with a personal or family history of medullary thyroid cancer. Pancreatitis is listed as a risk, though the meta-analysis in diabetes did not find an excess. Delayed stomach emptying has been linked to aspiration during anesthesia, and a small increase in diabetic retinopathy complications was seen in one diabetes trial. Loss of lean mass alongside fat, and the near-universal regain after stopping, are the practical concerns the trials have documented. ^1235712