What is Semaglutide?

Semaglutide is a medicine that mimics a hormone your gut naturally releases after a meal. It was developed by Novo Nordisk and is sold under three brand names: Ozempic (weekly injection for type 2 diabetes), Wegovy (weekly injection for weight management), and Rybelsus (a once-daily tablet for type 2 diabetes). All three contain the same active molecule^[1].

This page explains what semaglutide is, how it works in plain terms, what the trials have shown, and what its approval status looks like. It is for educational purposes only. It is not medical advice, and any decision about starting, stopping, or adjusting semaglutide belongs with a clinician who knows your medical history.

How it works

After you eat, your intestine releases a hormone called glucagon-like peptide-1 (GLP-1). GLP-1 signals to your pancreas to release insulin, tells your stomach to slow down digestion, and sends appetite-reducing messages to the brain. Semaglutide is a GLP-1 receptor agonist: it binds the same receptor that natural GLP-1 activates and produces the same effects^[6].

Natural GLP-1 is broken down in the bloodstream within a couple of minutes. Semaglutide lasts much longer. Novo Nordisk attached a fatty-acid chain to the molecule so it binds to albumin (a protein in blood), which protects it from breakdown and extends its activity to roughly one week. That is why the subcutaneous doses are taken just once a week.

The net effect is a combination of better blood-sugar control (more insulin when glucose is high, less glucagon), slower gastric emptying, and reduced appetite. The appetite effect in particular is why semaglutide at higher doses produces substantial weight loss even in people who do not have diabetes.

What the evidence shows

In the STEP-1 trial, 1,961 adults with obesity or overweight who did not have diabetes were randomised to 2.4 mg semaglutide weekly or placebo for 68 weeks. The semaglutide group lost an average of 14.9% of body weight, compared with 2.4% on placebo^[3]. That difference is clinically meaningful: losing 15% of starting weight at that scale had not been seen in a drug trial before 2021.

The cardiovascular picture has two separate sets of evidence. For people with type 2 diabetes, SUSTAIN-6 followed 3,297 patients at high cardiovascular risk for about two years and found the rate of major adverse cardiovascular events was 6.6% with semaglutide versus 8.9% with placebo^[5]. For people with obesity but without diabetes, the SELECT trial enrolled more than 17,000 patients and found a 20% relative reduction in major adverse cardiovascular events (hazard ratio 0.80)^[4]. SELECT is the reason the FDA and the EMA have extended Wegovy's indication to include cardiovascular risk reduction.

Approved uses

The EMA authorised Ozempic in February 2018 for type 2 diabetes in adults. Wegovy received EMA authorisation in January 2022 for weight management in adults with BMI of 30 or above, or BMI of 27 or above with at least one weight-related condition^[2]. The FDA has issued equivalent approvals for both indications. Rybelsus (oral semaglutide) is authorised for type 2 diabetes in both the US and the EU.

Regulatory status varies by country. Per-country detail on prescribing rules, reimbursement, and availability is on the semaglutide regulation pages. The short version: semaglutide is prescription-only everywhere PeptideMethods covers. It is not available over the counter and is not a supplement.

Side effects and contraindications

The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, and constipation. These are typically most pronounced during dose escalation and tend to ease as the body adjusts^[6]. In the STEP-1 trial, 4.5% of participants in the semaglutide group discontinued because of gastrointestinal events, compared with 0.8% on placebo^[3].

Semaglutide carries a boxed warning in both the US and EU for a risk of thyroid C-cell tumours seen in rodent studies. It is contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. A full list of contraindications and drug interactions is in the official prescribing information linked in the sources below. Discuss your personal risk factors with a prescriber before starting any semaglutide product.

What semaglutide is not

Semaglutide is not a peptide in the research-chemical or bodybuilding sense. It is a regulated prescription medicine. There are no approved generic versions as of mid-2026, and loose vials labelled "semaglutide for research use only" sold online are not the same product and have been the subject of counterfeit warnings from the EMA, MHRA, and FDA. The compounded semaglutide shortage exception in the US has also closed: the FDA declared the shortage resolved and compounding pharmacies are no longer authorised to prepare bulk semaglutide copies under 503A or 503B enforcement discretion.

For a comparison of semaglutide with the next-generation dual agonist, see the semaglutide vs tirzepatide overview.