What Is Semaglutide? A Complete Overview

Semaglutide has become one of the most widely discussed medications in recent years. Originally developed for type 2 diabetes, it has since gained attention for its effects on weight loss, cardiovascular risk, and metabolic health more broadly. But the sheer volume of media coverage can make it difficult to separate the clinical reality from the noise. This article breaks down what semaglutide actually is, how it works, and what the research says.

The basics: what semaglutide does in the body

Semaglutide is a synthetic analog of a naturally occurring hormone called glucagon-like peptide-1, or GLP-1. Your gut releases GLP-1 after you eat. It tells the pancreas to produce insulin, suppresses glucagon (a hormone that raises blood sugar), and slows the rate at which food leaves the stomach. All of these actions help regulate blood sugar levels.

The problem with natural GLP-1 is that it breaks down within minutes. Semaglutide was engineered to resist that degradation. Through modifications to the peptide chain and the addition of a fatty acid side chain that binds to albumin in the blood, semaglutide has a half-life of roughly seven days. That is why Ozempic and Wegovy are dosed once per week.

Beyond the pancreas, GLP-1 receptors are found in multiple areas of the brain, particularly the hypothalamus and brainstem regions involved in appetite regulation. Semaglutide crosses the blood-brain barrier and acts on these receptors, which is thought to be the primary mechanism behind the appetite suppression and food preference changes that many patients report.

FDA-approved formulations

Semaglutide is the active ingredient in three distinct FDA-approved products, each with its own indication:

• Ozempic (injectable, 0.5 mg, 1 mg, or 2 mg weekly): Approved for type 2 diabetes management and cardiovascular risk reduction in adults with type 2 diabetes and established heart disease.
• Wegovy (injectable, 2.4 mg weekly): Approved for chronic weight management in adults with obesity (BMI of 30 or greater) or overweight (BMI of 27 or greater) with at least one weight-related condition.
• Rybelsus (oral tablet, 7 mg or 14 mg daily): Approved for type 2 diabetes. The oral formulation uses an absorption enhancer called SNAC to allow the peptide to survive the stomach and enter the bloodstream through the gastric lining.

All three contain semaglutide. The differences come down to dosing, route of administration, and the specific conditions for which they have been studied and approved.

The clinical trial evidence

The evidence base for semaglutide is extensive. The SUSTAIN program (Semaglutide Unabated Sustainability in Treatment of Type 2 Diabetes) included more than 8,000 patients across multiple trials and established the drug's efficacy for glycemic control. In these trials, semaglutide at the 1 mg dose reduced HbA1c by an average of 1.5 to 1.8 percentage points compared to baseline, depending on the study and comparator.

The STEP program (Semaglutide Treatment Effect in People with Obesity) examined the 2.4 mg dose specifically for weight management. STEP 1, published in the New England Journal of Medicine in 2021, enrolled 1,961 adults without diabetes who had a BMI of 30 or higher. Over 68 weeks, participants receiving semaglutide lost an average of 14.9% of their body weight, compared to 2.4% in the placebo group. That translated to roughly 33 pounds on average.

STEP 2 looked at adults with type 2 diabetes and obesity. Weight loss was somewhat lower at 9.6% of body weight, which is consistent with the general finding that patients with diabetes tend to lose less weight on GLP-1 medications than those without diabetes.

Perhaps the most significant recent trial is SELECT (Semaglutide Effects on Cardiovascular Outcomes in People with Overweight or Obesity), published in the New England Journal of Medicine in 2023. This trial enrolled 17,604 adults aged 45 and older who had overweight or obesity and established cardiovascular disease but not diabetes. Over a median follow-up of 39.8 months, semaglutide 2.4 mg reduced the risk of major adverse cardiovascular events (MACE) by 20% compared to placebo. This was noteworthy because it demonstrated cardiovascular benefit independent of diabetes.

How it compares to other GLP-1 medications

Semaglutide is not the only GLP-1 receptor agonist on the market. Liraglutide (Victoza, Saxenda) was the previous generation and requires daily injection. Dulaglutide (Trulicity) is another weekly option. In head-to-head trials, semaglutide has generally shown superior A1C reduction and greater weight loss compared to these older agents.

Tirzepatide (Mounjaro, Zepbound) is a newer medication that activates both GLP-1 and GIP receptors. In the SURPASS and SURMOUNT clinical programs, tirzepatide produced greater weight loss than semaglutide at the highest doses, with average reductions of up to 22.5% of body weight in SURMOUNT-1. However, tirzepatide's cardiovascular outcomes data are still being collected, while semaglutide has completed cardiovascular outcome trials in both diabetic and non-diabetic populations.

Side effects and tolerability

The most common side effects are gastrointestinal: nausea, vomiting, diarrhea, and constipation. In the STEP 1 trial, nausea occurred in about 44% of participants on semaglutide, compared to 17% on placebo. Most episodes were mild to moderate and tended to resolve after the first 8 to 12 weeks as the dose was escalated.

Serious but less common risks include pancreatitis, gallbladder disease, and potential worsening of diabetic retinopathy (observed in SUSTAIN 6). The FDA prescribing information also carries a boxed warning about thyroid C-cell tumors based on findings in rodent studies, though this has not been confirmed in humans.

There are ongoing discussions in the medical community about muscle loss during rapid weight loss, changes in facial appearance (sometimes called "Ozempic face"), and the question of what happens when patients stop the medication. STEP 1 extension data showed that participants regained approximately two-thirds of the weight they had lost within one year of stopping semaglutide, which has raised important questions about the long-term treatment model.

The bottom line

Semaglutide is a well-studied GLP-1 receptor agonist with robust clinical trial data supporting its use in type 2 diabetes, chronic weight management, and cardiovascular risk reduction. It is not a cosmetic drug, and it is not without side effects. For patients with legitimate metabolic conditions, however, the data from the SUSTAIN, STEP, and SELECT programs represent some of the strongest evidence for any medication in its class.

If you are considering semaglutide, the most productive step is a conversation with your physician about your specific medical history, goals, and insurance coverage. The right medication depends on your individual circumstances, not on headlines.