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The basics

What is semaglutide? Ozempic, Wegovy and Rybelsus explained in plain English

Semaglutide is the active ingredient in Ozempic, Wegovy and Rybelsus. Here is what it is, what it is made of, what each brand is approved for, how long it stays in the body, and what the big trials found.

By 7 min read
Illustration of an unbranded pen beside a calendar.
The short version
  • Semaglutide is a weekly or daily GLP-1 medicine, a lab-made copy of a gut hormone that is 94% identical to the body's own version. It is sold as Ozempic, Wegovy and Rybelsus.1
  • It lasts a long time: the label gives a half-life of about 1 week, so it stays in the blood for about 5 to 7 weeks after the last dose.1
  • In the STEP 1 trial, adults with obesity and no diabetes lost an average of 14.9% of body weight over 68 weeks, vs 2.4% on placebo.4

What is semaglutide?

Semaglutide is a medicine that copies GLP-1, a hormone your gut releases after you eat. It is a GLP-1 receptor agonist. A receptor is a docking spot on a cell, and an agonist is a drug that switches on the same receptor the body's own hormone does. Switching on GLP-1 receptors helps the body release insulin when blood sugar is high and turns down appetite through the brain.1,2 Semaglutide is the generic name. Ozempic, Wegovy and Rybelsus are brand names for the same active ingredient.

A simple way to picture it: your own GLP-1 is like a doorbell that rings briefly after a meal. Semaglutide is a near-copy of the finger pressing that bell, built to keep pressing for days. The analogy stops working because the body does not just "hear" the signal once. It affects insulin, appetite and how fast the stomach empties, and the effects change over weeks.

New to these terms? Our plain-English guide to GLP-1 explains the hormone itself.

Illustration of a tablet next to a glass of water.

What is semaglutide made of?

Semaglutide is a peptide, which means a short chain of amino acids, the building blocks of protein. The US label says it has 94% sequence homology to human GLP-1, meaning 94% of its chain matches the natural hormone.1

The label lists three changes that make it last:1,2

  • A fatty acid side chain. It lets semaglutide stick to albumin, a common protein in the blood. While attached, it is protected and the kidneys clear it slowly.
  • A swap at position 8. This protects it from DPP-4, an enzyme that breaks down natural GLP-1.
  • Made by yeast. The peptide backbone is produced by yeast fermentation.

The Ozempic pen solution also contains inactive ingredients: disodium phosphate, propylene glycol, phenol and water.2 The tablets contain SNAC (salcaprozate sodium), an absorption enhancer that helps the peptide get through the stomach wall.3

Semaglutide brands and what each is approved for

BrandFormUS approved uses (label section 1)
Ozempic injectionWeekly penBlood sugar control in adults with type 2 diabetes; lowering the risk of heart attack, stroke and heart-related death in adults with type 2 diabetes and heart disease; lowering the risk of kidney decline, kidney failure and heart-related death in adults with type 2 diabetes and chronic kidney disease
Wegovy injectionWeekly pen or prefilled syringeLong-term weight management in adults with obesity, or overweight plus at least one weight-related condition, and in children 12 and older with obesity; lowering heart attack, stroke and heart-related death in adults with heart disease and obesity or overweight; MASH (a form of fatty liver disease) with moderate to advanced scarring, under accelerated approval
Wegovy tabletsDaily tabletLong-term weight management in adults, and lowering heart risk in adults with heart disease and obesity or overweight
Rybelsus and Ozempic tabletsDaily tabletBlood sugar control in adults with type 2 diabetes; lowering heart risk in adults with type 2 diabetes at high risk
 Sources: Wegovy, Ozempic, and Rybelsus/Ozempic tablets US labels, section 1.1–3 Weight-loss uses always come with a reduced-calorie diet and more physical activity.

The pens and tablets come in different strengths. Wegovy injection ranges from 0.25 mg to 7.2 mg per weekly dose, Rybelsus tablets come in 3, 7 and 14 mg, and Ozempic tablets in 1.5, 4 and 9 mg (label section 11).1,3 The label for the tablets says Rybelsus and Ozempic tablets are not interchangeable milligram for milligram.3 Which brand and dose fits a person is a decision for their prescriber. For how the brands compare, see Ozempic vs Wegovy vs Mounjaro vs Zepbound and our piece on semaglutide tablets for weight loss.

How long does semaglutide last in the body?

Half-life is the time it takes for half of a drug to leave the blood. The labels' pharmacokinetics section (12.3) gives semaglutide an elimination half-life of about 1 week.1,2 That is why the injection is taken once a week. It also means the medicine lingers: the Wegovy label says semaglutide is present in the blood for about 5 to 7 weeks after the last 2.4 mg or 7.2 mg injection or 25 mg tablet, and the Ozempic label says about 5 weeks.1,2 More on this in our GLP-1 half-life explainer.

What did the big trials find?

−14.9%average weight change at 68 weeks on semaglutide 2.4 mg vs −2.4% on placebo, STEP 1, 1,961 adults without diabetes
6.5% vs 8.0%had a heart attack, stroke or heart-related death, semaglutide vs placebo, SELECT, 17,604 adults with heart disease

STEP 1 (weight). Adults with a BMI of 30 or more, or 27 or more with a weight-related condition, and no diabetes took weekly semaglutide 2.4 mg or placebo for 68 weeks, with lifestyle counseling. Average weight fell 14.9% on semaglutide and 2.4% on placebo. 86.4% of people on semaglutide lost at least 5% of their weight, vs 31.5% on placebo.4 See GLP-1 weight loss results for more trials.

SELECT (heart). This trial enrolled 17,604 adults aged 45 or older with existing heart disease, a BMI of 27 or more and no diabetes. Over about 40 months of follow-up, a heart attack, stroke or heart-related death happened to 6.5% on semaglutide 2.4 mg and 8.0% on placebo, a hazard ratio of 0.80, or about 20% lower risk.5 Details in our SELECT trial explainer.

What about compounded semaglutide, with glycine or B12?

Compounded semaglutide is made by a pharmacy rather than the manufacturer. The FDA says compounded drugs are not FDA approved, which means the agency does not review them for safety, effectiveness or quality before they are sold.6 Some compounded products add other ingredients. A 2026 review of 33 compounded semaglutide and tirzepatide products found that 48% combined the drug with ingredients such as B12 (cyanocobalamin), glycine, niacinamide, docusate or ondansetron. The authors found little justification for adding nutrients.7 More in compounded semaglutide and tirzepatide.

Side effects and the boxed warning

The most common side effects in the labels are stomach-related. For Ozempic, those reported in at least 5% of patients are nausea, vomiting, diarrhea, belly pain and constipation.2 The Wegovy list is longer and also includes headache, tiredness, indigestion, dizziness, burping, reflux and hair loss.1 In STEP 1, nausea and diarrhea were usually mild to moderate and eased over time, and 4.5% of people on semaglutide stopped because of stomach side effects, vs 0.8% on placebo.4

All semaglutide labels carry a boxed warning, the FDA's strongest, about thyroid C-cell tumors. Semaglutide caused these tumors in rodents, and it is unknown whether it does in humans. The labels say not to use it if you or a family member has had medullary thyroid cancer or if you have MEN 2.1 The labels also list serious risks such as pancreatitis and gallbladder problems. A lump in the neck, trouble swallowing, or severe belly pain that will not go away needs prompt medical attention.

For practical tips, see nausea on GLP-1s and GLP-1s and thyroid cancer.

Key terms in this article

  • GLP-1: a gut hormone released after eating that helps control blood sugar and appetite.
  • Receptor agonist: a drug that switches on the same receptor (cell docking spot) as a natural hormone.
  • Peptide: a short chain of amino acids, the building blocks of protein.
  • Albumin: a common blood protein; semaglutide sticks to it, which slows its removal.
  • Half-life: the time it takes for half of a drug to leave the blood.
  • Compounded drug: a version mixed by a pharmacy, not reviewed or approved by the FDA.
  • Boxed warning: the FDA's most serious type of label warning.

Common questions

What is semaglutide used for?

In the US, semaglutide is approved for type 2 diabetes (Ozempic, Rybelsus), for long-term weight management in adults and children 12 and older with obesity (Wegovy injection), and to lower the risk of heart attack, stroke and heart-related death in certain adults. Wegovy injection is also approved for a form of fatty liver disease called MASH with moderate to advanced scarring.

What is semaglutide the generic for?

Semaglutide is the generic name of the active ingredient. Ozempic, Wegovy and Rybelsus are brand names for it, all made by Novo Nordisk, and they differ in form, strength and approved uses.

What is semaglutide made of?

Semaglutide is a peptide, a short chain of amino acids, that is 94% identical in sequence to the body's own GLP-1 hormone, according to the US label. Its backbone is made by yeast fermentation, and a fatty acid side chain lets it stick to a blood protein called albumin, which is why it lasts about a week.

How much weight do people lose on semaglutide?

In the 68-week STEP 1 trial of 1,961 adults with obesity or overweight and no diabetes, people on weekly semaglutide 2.4 mg lost an average of 14.9% of body weight, compared with 2.4% on placebo. Both groups also had lifestyle counseling.

What is semaglutide with glycine or B12?

These are compounded versions made by pharmacies, not FDA-approved products. A 2026 review of 33 compounded semaglutide and tirzepatide products found that 48% added ingredients such as B12 or glycine, and its authors found little justification for adding nutrients.

Sources

  1. WEGOVY (semaglutide) injection and tablets. US prescribing information, sections 1, 6, 11, 12.1 and 12.3 and boxed warning. Novo Nordisk. DailyMed, version effective June 18, 2026. DailyMed
  2. OZEMPIC (semaglutide) injection. US prescribing information, sections 1, 6, 11, 12.1 and 12.3. Novo Nordisk. DailyMed, version effective June 1, 2026. DailyMed
  3. RYBELSUS and OZEMPIC (semaglutide) tablets. US prescribing information, sections 1, 2 and 11. Novo Nordisk. DailyMed, version effective January 30, 2026. DailyMed
  4. Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed · doi:10.1056/NEJMoa2032183
  5. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232. PubMed · doi:10.1056/NEJMoa2307563
  6. US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Content current as of October 1, 2026. fda.gov
  7. Belcourt J, Sapowadia A, White CM. Compounded Semaglutide and Tirzepatide Products Use Unique Formulations but Efficacy and Safety Largely Unknown. Ann Pharmacother. 2026;60(9):902-906. PubMed · doi:10.1177/10600280261421979
This article summarises published research for general information. It is not medical advice and does not replace advice from your own care team. Never change a medication or dose without talking to your prescriber.

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