Semaglutide Research: STEP & SELECT Data

Summary

Semaglutide is a GLP-1 receptor agonist approved for type 2 diabetes, chronic weight management and cardiovascular risk reduction in people with obesity and established cardiovascular disease. The STEP and SELECT programmes gave the class its first hard-outcome evidence, moving it beyond weight and glucose endpoints.

Last reviewed 2026-09-01

What it is

Semaglutide is an analogue of human GLP-1 with 94% sequence homology, modified at position 8 to resist DPP-4 degradation and carrying a C18 fatty diacid linker that binds albumin, giving a half-life of about one week.

Developed by Novo Nordisk following liraglutide, approved for type 2 diabetes in 2017 (Ozempic), oral formulation in 2019 (Rybelsus), and for chronic weight management in 2021 (Wegovy).

Synthetic analogue of the endogenous incretin hormone GLP-1, which is secreted by intestinal L-cells after eating.

It produced weight reductions previously achievable only with bariatric surgery in a subset of patients, and then demonstrated cardiovascular event reduction in people without diabetes.

How it works

In plain terms

Semaglutide mimics a gut hormone released after eating. It tells the brain that you are full, slows how fast the stomach empties, and helps the pancreas release insulin only when glucose is high.

Technical detail

GLP-1 receptor agonism in the hypothalamic arcuate nucleus and area postrema reduces energy intake; peripheral effects include delayed gastric emptying, glucose-dependent insulin secretion and glucagon suppression. GLP-1 receptors are also present on cardiac, renal and vascular tissue, and anti-inflammatory and endothelial effects are proposed as contributors to the cardiovascular outcome findings, independent of weight change.

Pathways involved

Hypothalamic and area postrema appetite regulation
Delayed gastric emptying
Glucose-dependent insulin secretion, glucagon suppression
Vascular and renal GLP-1 receptor signalling

Current research

Laboratory research

Receptor binding, albumin affinity and DPP-4 resistance are fully characterised; the pharmacokinetic design is textbook.

Animal research

Rodent studies established appetite and glycaemic effects, and produced the thyroid C-cell tumour findings that underpin the class boxed warning.

Human research

STEP-1 reported about 14.9% mean weight reduction at 68 weeks on 2.4 mg. SELECT reported a 20% reduction in major adverse cardiovascular events in people with overweight or obesity and established cardiovascular disease but without diabetes. FLOW reported kidney outcome benefits in type 2 diabetes with chronic kidney disease. Trials in heart failure with preserved ejection fraction and in metabolic dysfunction-associated steatohepatitis have also reported positive findings.

Ongoing research

Programmes in Alzheimer's disease, addiction-related endpoints and peripheral arterial disease are the most watched current threads.

What is being investigated

Chronic weight management (approved)
Type 2 diabetes glycaemic control (approved)
Cardiovascular event reduction (approved in several markets)
Chronic kidney disease progression
Metabolic dysfunction-associated steatohepatitis
Neurodegenerative and addiction endpoints (exploratory)

These are research directions reported in the literature, not established effects or recommendations.

Risks, limitations and unknowns

Read this section before the rest

Gastrointestinal adverse events are common, especially during dose escalation
Boxed warning for thyroid C-cell tumours from rodent data; contraindicated with medullary thyroid carcinoma history or MEN2
Pancreatitis and gallbladder events reported; gallstone risk rises with rapid weight loss generally
Rare reports of non-arteritic anterior ischaemic optic neuropathy are under regulatory review
Significant lean mass loss is documented; regain after discontinuation was around two-thirds of lost weight within a year in STEP-1 extension

Evidence ratings

Laboratory studies

Strong

Mechanism and pharmacokinetics fully characterised.

Animal studies

Strong

Extensive; also the source of the C-cell tumour signal.

Human studies

Strong

Large Phase 3 programme plus hard cardiovascular outcome data.

Long-term safety

Moderate

Multi-year randomised data; post-marketing surveillance ongoing.

Comparisons

Tirzepatide vs Semaglutide

Cagrilintide vs Semaglutide

References

[1]STEP-1 weight management trial — PubMed / NEJM, 2021
[2]SELECT cardiovascular outcomes — PubMed / NEJM, 2023
[3]FLOW kidney outcomes — PubMed / NEJM, 2024
[4]Registered semaglutide trials — ClinicalTrials.gov, current
Reference links open searches and records on PubMed and ClinicalTrials.gov so that every statement above can be traced to primary literature.

Frequently asked questions

What is semaglutide?+

A GLP-1 receptor agonist — a modified analogue of the human incretin hormone GLP-1 — with a one-week half-life.

Is semaglutide FDA approved?+

Yes, for type 2 diabetes, chronic weight management, and cardiovascular risk reduction in adults with obesity and established cardiovascular disease.

How much weight loss did STEP-1 report?+

Approximately 14.9% mean reduction at 68 weeks on 2.4 mg weekly, versus about 2.4% on placebo.

What did the SELECT trial show?+

A 20% relative reduction in major adverse cardiovascular events in people with overweight or obesity and prior cardiovascular disease, without diabetes.

Is Ozempic a peptide?+

Yes. Semaglutide is a 31–amino-acid peptide analogue with a fatty acid side chain.

How does semaglutide differ from tirzepatide?+

Semaglutide acts on one receptor (GLP-1); tirzepatide acts on two (GLP-1 and GIP) and produced larger reductions in head-to-head trials.

Does semaglutide work orally?+

Yes, in a formulation using the absorption enhancer SNAC, though bioavailability is low and dosing requirements are strict.

What happens when you stop?+

The STEP-1 extension found participants regained about two-thirds of lost weight within a year of stopping.

Are the eye safety reports confirmed?+

Rare cases of non-arteritic anterior ischaemic optic neuropathy have been reported and reviewed by regulators; a causal relationship has not been established.

Continue your research

Tirzepatide research

Cagrilintide research

Incretin side effects