What Is Semaglutide and How Does It Work?
Semaglutide is a prescription GLP-1 receptor agonist — a drug that mimics a gut hormone called GLP-1 to lower blood sugar and reduce appetite. It’s the active ingredient in three FDA-approved brand-name medications made by Novo Nordisk: Ozempic and Rybelsus for type 2 diabetes, and Wegovy for chronic weight management. It works by activating GLP-1 receptors in the pancreas, gut, and brain, which prompts the body to release insulin when blood sugar is high, slows how fast food leaves the stomach, and quiets appetite signals in the hypothalamus.
What Is Semaglutide?
A synthetic version of a hormone your gut already makes, engineered to last a full week in the body.
Semaglutide is a glucagon-like peptide-1 (GLP-1) analogue — a lab-made molecule that closely resembles a natural gut hormone. FDA prescribing information describes it as sharing 94% of its amino-acid sequence with human GLP-1. That similarity is what lets it fit into the same receptors your body’s own GLP-1 uses.
The remaining differences are what make it a medication rather than a fleeting hormone. Natural GLP-1 gets broken down within minutes by an enzyme called DPP-4. Semaglutide is engineered to resist that enzyme and to bind to a protein in your blood called albumin, which shields it from being cleared by the kidneys. The result is a half-life long enough that a single injection keeps working for about a week.
All three semaglutide brands are made by Novo Nordisk. There is no FDA-approved generic semaglutide as of August 2026 — the patent still holds. If you’ve seen “generic semaglutide” advertised, that’s almost always compounded semaglutide from a licensed compounding pharmacy, which is a separate product category with different rules and different risks.
How Does Semaglutide Work in Your Body?
It activates GLP-1 receptors in three places at once — pancreas, stomach, and brain — and each one does something different.
GLP-1 is a hormone your intestines release after you eat. It’s what your body normally uses to tell the pancreas to release insulin, tell the stomach to slow down, and tell the brain you’re full. Semaglutide switches those same signals on and holds them on.
In the pancreas. Semaglutide prompts insulin release only when blood sugar is elevated — a mechanism called glucose-dependent secretion. It also lowers glucagon, the hormone that raises blood sugar between meals. Together, that pulls blood sugar down without the drop-into-the-basement risk of some older diabetes drugs.
In the stomach and small intestine. It slows gastric emptying, meaning food sits in the stomach longer after a meal. That flattens the spike of sugar entering the bloodstream, and it’s a big part of why people feel full sooner and stay full longer.
In the brain. This is where the weight-loss effect largely comes from. GLP-1 receptors in the hypothalamus and brainstem regulate appetite and reward. When semaglutide activates them, hunger drops, cravings quiet down, and people tend to eat less at each meal without white-knuckling it. Many describe it as “food noise” going away.
The full weight-loss and blood-sugar effects don’t show up on day one. Semaglutide is dosed in a step-up schedule, and clinical results build over months. For a week-by-week breakdown, see How long does semaglutide take to work.
What Is Semaglutide Approved For?
Three brand-name products, same molecule, different FDA-approved uses and doses.
| Brand | Form | FDA-approved uses | First approved |
|---|---|---|---|
| Ozempic | Weekly injection (0.25–2.0 mg) | Type 2 diabetes; reducing risk of major cardiovascular events in adults with T2D and heart disease; reducing risk of kidney function decline in T2D | December 2017 |
| Rybelsus | Daily oral tablet (3, 7 or 14 mg) | Type 2 diabetes; reducing risk of major cardiovascular events in adults with T2D and heart disease | September 2019 |
| Wegovy (injection) | Weekly injection (0.25–2.4 mg) | Chronic weight management in adults and children 12+ with obesity (or overweight with a weight-related condition); reducing risk of major cardiovascular events; non-cirrhotic MASH (metabolic-dysfunction-associated steatohepatitis) | June 2021 |
| Wegovy (oral) | Daily oral tablet (25 mg) | Chronic weight management in adults with obesity (or overweight with a weight-related condition) | December 2025 |
Same molecule doesn’t mean interchangeable. The dose that treats type 2 diabetes (Ozempic tops out at 2.0 mg weekly) is lower than the dose approved for weight loss (Wegovy goes to 2.4 mg weekly), which is why prescribing a diabetes brand off-label for weight loss isn’t the same product you’d get from the weight-loss brand.
Off-brand comparisons come up constantly — if you’re trying to sort out whether Wegovy, Ozempic, and generic semaglutide are actually the same drug, we walk through it in Is Wegovy the same as semaglutide.
Who Can Take Semaglutide?
FDA labeling narrows eligibility more than most people expect. Two different sets of criteria depending on which brand.
For weight management (Wegovy). The label covers adults with a BMI of 30 or higher (obesity), or a BMI of 27 or higher (overweight) with at least one weight-related condition such as high blood pressure, type 2 diabetes, or high cholesterol. Injectable Wegovy is also approved for children aged 12 and older with obesity. The new oral Wegovy tablet (December 2025) is currently approved for adults only.
For type 2 diabetes (Ozempic, Rybelsus). Approved as an add-on to diet and exercise to improve blood-sugar control in adults with type 2 diabetes. Not approved for type 1 diabetes.
Who should not take it. FDA labeling for all three brands carries a boxed warning about thyroid C-cell tumors (based on rodent studies), and lists a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) as a contraindication. Pregnancy is another contraindication. A prescribing provider is the one who screens for these — that’s part of what a real telehealth intake should cover, not a checkbox after the fact.
What you’ll actually pay is a separate question. Cash price runs about $1,000–$1,350/month at brand pharmacy without coverage; with commercial insurance and manufacturer savings, some people pay as little as $25/month. Full breakdown: Wegovy and Zepbound savings cards and the GLP-1 insurance coverage checker.
What Are the Main Side Effects?
Same mechanism that helps with appetite is what causes most of the discomfort.
The most common side effects across all three semaglutide brands are gastrointestinal: nausea, vomiting, diarrhea, constipation, and stomach pain. These usually cluster around dose increases and tend to fade as the body adjusts. Nausea in particular is often worst in the first month or two.
Less common but serious effects listed in FDA labeling include pancreatitis, gallbladder problems, kidney injury (often linked to dehydration from vomiting or diarrhea), diabetic retinopathy complications in people with pre-existing eye disease, and low blood sugar — more of a risk when semaglutide is combined with insulin or a sulfonylurea.
For a fuller timeline of what shows up when, and what usually helps, see Semaglutide side effects: timeline and what eases them.