Semaglutide across clinical populations
Heart disease, diabetes, kidney disease: the eligibility criteria decide who enters each experiment and what can be learned there.
Cardiovascular disease, with and without diabetes
In SELECT, 17,604 adults had cardiovascular disease and overweight or obesity, without diabetes. Semaglutide reduced the combined risk of cardiovascular death, nonfatal heart attack or nonfatal stroke by 20% relative to placebo. The percentage concerns that combined outcome.
SUSTAIN-6 studied 3,297 adults with type 2 diabetes at high cardiovascular risk and found a 26% relative reduction in the same type of cardiovascular composite. Diabetic-retinopathy complications were more frequent with semaglutide. Existing eye disease and rapid improvement in blood sugar help frame that finding in the safety literature.
I read these trials together because the eye result makes the people in the experiment impossible to treat as background information. The cardiovascular findings deserve attention in both groups; diabetes also brings a specific complication into the safety account. Comparing the two percentages alone would miss that.
Weight and kidney measurements
STEP 1 enrolled 1,961 adults with overweight or obesity and no diabetes. At 68 weeks, mean weight change was −14.9% with semaglutide and −2.4% with placebo. The study used semaglutide 2.4 mg once weekly; these are the investigators’ treatment conditions.
FLOW enrolled 3,533 adults with type 2 diabetes and chronic kidney disease. Semaglutide 1.0 mg reduced the primary kidney composite risk by 24% relative to placebo. That composite included kidney failure, a major fall in kidney function, and kidney-related or cardiovascular death. It was a broader outcome than kidney function alone.
The first result describes weight in adults without diabetes; the second concerns serious events in adults with both diabetes and kidney disease. I prefer the extra space those descriptions take to a single sweeping claim about metabolic health.
A molecule and two formulations
Semaglutide is a 31-amino-acid analogue of the gut hormone GLP-1. Structural changes slow enzymatic breakdown and let a fatty side chain bind reversibly to albumin in blood, extending its stay to roughly a week. It increases insulin release when glucose is high, suppresses inappropriate glucagon release and slows gastric emptying.
Swallowing creates a different obstacle. The oral formulation contains an absorption helper that locally protects the peptide and assists passage across the stomach lining; less than 1% reaches the blood. The safety review discusses the oral and injectable formulations. The oral formulation solves an absorption problem I had underestimated; the injections used in the trials above remain the conditions behind those numerical results.
The appetite-pathway experiments were conducted in mice and rats. They found reduced food intake and altered food preference without a reduction in energy expenditure. Those animal brain findings help investigate a mechanism; they leave the corresponding human brain effects to human study.
Semaglutide warnings
The dedicated safety review found an overall favourable benefit-risk profile in type 2 diabetes, with gastrointestinal effects leading the adverse-event account. Nausea, vomiting, diarrhea and constipation can limit treatment. Gallbladder and biliary disease were increased; pancreatitis remains a label warning. Rodent thyroid C-cell tumours underlie a boxed warning, and personal or family history of medullary thyroid carcinoma or MEN-2 is a contraindication. Human data have not established a clear thyroid-cancer increase.
Community accounts add quieter food thoughts, changed tastes, foul-smelling burps, tiredness, constipation and hair shedding. These accounts are anecdotal and cannot establish clinical effects or their causes. Those intrusive symptoms sound miserable to me; a list of reported symptoms still cannot estimate the risk for a particular person. Weight loss can include lean tissue, and weight can return after stopping treatment.
Approved uses include type 2 diabetes, chronic weight management, cardiovascular risk reduction in adults with established cardiovascular disease and excess weight, and MASH since 2025. MASH involves liver inflammation and scarring associated with fat accumulation. The existence of approved formulations does not extend their approval to research material or every preparation bearing the same ingredient name. Tirzepatide’s direct comparisons are worth reading with their separate trial conditions alongside.