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Metabolic and incretin class
Semaglutide: What the Trials Showed, and Where It Sits Now
The short answer
Semaglutide is a long-acting copy of GLP-1, a gut hormone that tells the pancreas to release insulin and tells the brain you have eaten. It is an approved medicine with one of the largest trial programmes in modern metabolic medicine, covering blood sugar, weight, cardiovascular events and, since 2026, liver disease.
Questions people ask about Semaglutide
- What is semaglutide used for?
- Is semaglutide FDA approved?
- What is the difference between Ozempic and Wegovy?
- How much weight do people lose on semaglutide?
- Semaglutide vs tirzepatide: which is better?
- What are semaglutide’s side effects?
- Does semaglutide cause muscle loss?
- What happens when you stop semaglutide?
- Is compounded semaglutide the same?
- Is semaglutide banned in sport?
Semaglutide at a glance
| Also called | Ozempic, Wegovy, Rybelsus (brand names); GLP-1 receptor agonist |
|---|---|
| What it is | A 31-amino-acid analog of human GLP-1, modified to last about a week |
| Acts on | GLP-1 receptors in the pancreas, stomach and the appetite centres of the brain |
| Main system | Metabolic: appetite, insulin, blood glucose |
| Evidence level | Approved medicine: large Phase 3 programme plus cardiovascular outcome data |
| FDA status (Sept 2026) | Approved. Type 2 diabetes (2017), weight management (2021), cardiovascular risk reduction, liver disease with fibrosis, and an oral version for weight management (2026) |
| In sport | Not named on the 2026 WADA prohibited list |
What is semaglutide?
GLP-1 is a hormone your gut releases when food arrives. It nudges the pancreas to release insulin, slows how fast the stomach empties, and signals fullness to the brain. Natural GLP-1 is broken down within minutes.
Semaglutide is that hormone rebuilt to survive. The changes to its structure let it bind to albumin in the blood and resist the enzyme that would normally clear it, which is why one dose lasts about a week instead of a few minutes.
Metabolic Precision profiles it at pp. 97–98 and returns to it repeatedly through the incretin chapters (pp. 100–113), and Targeted Peptide Systems covers it at pp. 179–182.
How does semaglutide work?
Four effects, all from the same receptor:
- Insulin when it is needed. It increases insulin release in response to a meal rather than continuously, which is why it does not usually cause low blood sugar on its own.
- Less glucagon. It suppresses glucagon, the hormone that tells the liver to release stored sugar.
- Slower stomach emptying. Food leaves the stomach more slowly, which flattens the glucose rise after a meal and extends fullness.
- Appetite. It acts directly on appetite centres in the brain. Most people describe it as food simply mattering less, which is the effect that drives the weight results.
Metabolic Precision (pp. 69–73) sets out why this class sits at the base of a metabolic protocol: insulin resistance and visceral fat suppress the response to almost everything else, so correcting them first changes what the rest of a plan can do.
What does the research show?
Weight. STEP 1, published in the New England Journal of Medicine in 2021, randomised nearly 2,000 adults with overweight or obesity and reported about 15% average body weight loss at 68 weeks against about 2.4% on placebo (reference 1). That result is what moved this class from diabetes care into obesity medicine.
Cardiovascular events. SELECT, published in 2023, followed more than 17,000 adults with cardiovascular disease and overweight or obesity but no diabetes, and reported a 20% reduction in major adverse cardiovascular events over a mean of about 40 months (reference 2). This is the trial that made the case that the benefit is not only about the scale.
A pill that works. Oral semaglutide at 25 mg was tested in adults with overweight or obesity and published in the New England Journal of Medicine in 2025 (reference 3). The FDA approved the oral version for weight management in 2026, the first GLP-1 tablet cleared for that use.
Liver disease. In 2026 the FDA granted accelerated approval for non-cirrhotic metabolic dysfunction-associated steatohepatitis with moderate to advanced fibrosis, the first GLP-1 approved in that population.
Side effects and cautions
The common effects come from the mechanism rather than from anything exotic: nausea, vomiting, diarrhoea, constipation and reflux, usually worst while the dose is being raised and easing as the body adjusts. Slower stomach emptying is doing most of that work.
The less common but more serious signals discussed in the label and the literature are pancreatitis, gallbladder disease (more likely with rapid weight loss), and a rodent thyroid tumour finding that keeps the drug away from anyone with a personal or family history of medullary thyroid carcinoma or MEN2.
Two practical points the trials make plainly. Muscle is lost alongside fat unless protein intake and resistance training are deliberate, which is a protocol question rather than a drug problem. And weight regain after stopping is the norm in the trial data, so the exit plan matters as much as the start.
Metabolic Precision (pp. 108–113) works through how this class is sequenced with the rest of a protocol rather than bolted on to it.
Is semaglutide legal or FDA approved?
Approved, and widely prescribed. Semaglutide has been approved in the US since 2017 for type 2 diabetes and since 2021 for chronic weight management, with cardiovascular, oral and liver indications added since.
Compounded semaglutide is a different thing. While the drug was in official shortage, compounding pharmacies were permitted to prepare it. The FDA declared that shortage resolved in early 2025 and the permission ended. Product still sold as compounded or research semaglutide sits outside that framework, and salt forms such as semaglutide sodium are not the same molecule as the approved drug.
Sport: semaglutide is not named on the 2026 WADA prohibited list, though athletes should check with their own governing body, since lists are updated annually.
Semaglutide vs tirzepatide, retatrutide and the rest
The incretin compounds are best told apart by how many receptors they engage.
- vs tirzepatide: tirzepatide adds a second receptor, GIP. SURPASS-2 compared them head to head in type 2 diabetes and reported greater reductions in blood sugar and weight for tirzepatide (reference 4). Both are approved. See our tirzepatide profile.
- vs retatrutide: retatrutide adds a third, glucagon, and is still investigational. Its trial numbers are larger, and a trial result is not the same thing as an approved medicine with years of real-world data. See our retatrutide profile.
- vs the growth hormone compounds: a different axis entirely. Tesamorelin and the secretagogues work on body composition through growth hormone, not appetite, which is why the books treat them as separate layers rather than alternatives.
Our article on metabolism as an information system goes through how the books decide between these.
Risk, benefit, and the conversation this page is for
How to weigh it. Some research peptides have a quiet toxicology record, or an unfinished efficacy record. semaglutide is a different case: on its mechanism it genuinely moves physiology, in this case appetite, insulin signalling and how fast the stomach empties, and that is the reason to weigh it with due diligence rather than enthusiasm. Monitoring is paramount here, and the markers that matter are gastrointestinal tolerance, hydration, lean mass, and personal thyroid and pancreatic history.
The regulatory picture is moving, selectively. In July 2026 an FDA advisory committee recommended six peptides, BPC-157, TB-500, KPV, MOTS-c, Epitalon and Semax, for the list of bulk substances compounding pharmacies may use. Semaglutide is already approved, which is the far end of the same spectrum this library covers. What changed in 2025 is the other direction: once the official shortage ended, so did the permission for pharmacies to compound it. Reading those decisions one at a time is more useful than treating every compound outside the approved list as equivalent.
Why the class is taken seriously. This is one of the best-evidenced medicines in the whole library, with weight, cardiovascular and liver outcomes behind it. The open questions are about who it suits, what is protected while weight comes off, and what happens when it stops. The useful question is not whether engaging it does anything. It is whether you have done the due diligence to make an informed decision about engaging it at all: what your baseline looks like, what else you are taking, what you would measure along the way, and what would tell you to stop.
Which is the point of the series. Nothing here is a recommendation to use semaglutide. People misuse approved medicines and unapproved compounds alike, and that is neither the purpose nor the intent of this page. The point is a better conversation than the internet usually allows: with a clinician who knows your history, your labs and everything else you take, and who can help build a plan that fits you.
Semaglutide: frequently asked questions
What is semaglutide used for?
Type 2 diabetes, chronic weight management, reducing cardiovascular events in people with overweight or obesity and established cardiovascular disease, and, since 2026, non-cirrhotic liver disease with fibrosis.
Is semaglutide FDA approved?
Yes, since 2017 for type 2 diabetes and 2021 for weight management, with cardiovascular, oral and liver indications added since.
What is the difference between Ozempic and Wegovy?
The same molecule under different brand names and approved doses. Ozempic is licensed for type 2 diabetes, Wegovy for weight management.
How much weight do people lose on semaglutide?
In STEP 1, about 15% of body weight on average at 68 weeks, against about 2.4% on placebo (reference 1). Individual results vary widely around that average.
Semaglutide vs tirzepatide: which is better?
In the one head-to-head trial in type 2 diabetes, tirzepatide produced larger reductions in blood sugar and weight (reference 4). Both are approved, and tolerance differs between people, so the average is not the whole answer.
What are semaglutide’s side effects?
Mostly gastrointestinal: nausea, vomiting, diarrhoea, constipation and reflux, usually worst while the dose is increasing. Less common concerns include pancreatitis and gallbladder disease, and it is avoided in people with a history of medullary thyroid carcinoma or MEN2.
Does semaglutide cause muscle loss?
Some lean mass is lost alongside fat, as with most weight loss. Protein intake and resistance training are how that is addressed, which Metabolic Precision treats as part of the protocol rather than an afterthought.
What happens when you stop semaglutide?
Weight regain is the usual pattern in the trial data, because appetite returns to where it was. That is why the books treat the exit plan as part of the protocol.
Is compounded semaglutide the same?
No. Compounding was permitted during the official shortage, which the FDA declared resolved in early 2025. Material sold outside that framework, including salt forms such as semaglutide sodium, is not the approved drug.
Is semaglutide banned in sport?
It is not named on the 2026 WADA prohibited list. Check with your sport’s governing body, since lists change each year.
Where Semaglutide appears in our books
This page is the plain-language overview. The books go further: mechanism detail, evidence tiers, how Semaglutide fits a full protocol, and the cautions that go with it. Page numbers refer to the print editions.
Books marked Look Inside include these exact pages in their free preview.
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See how Semaglutide fits a protocol
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Open the Protocol BuilderSee the book seriesReferences
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989–1002. View sourceCited in Targeted Peptide Systems (reference 31)
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221–2232. View sourceThe SELECT trial
- Wharton S, Lingvay I, Bogdanski P, et al. Oral semaglutide at a dose of 25 mg in adults with overweight or obesity. N Engl J Med. 2025;393(11):1077–1087. View source
- Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503–515. View sourceCited in Targeted Peptide Systems (reference 36)
- World Anti-Doping Agency. The 2026 Prohibited List. View source
How this page is maintained. Regulatory status and trial results change. We review this page against current sources and update it as new information becomes available; the date at the top shows the last review.
Educational information only, not medical advice. Semaglutide is discussed here for education. Nothing on this page is a recommendation to use it or a dosing guide. Talk to a qualified clinician before starting, stopping or combining any compound.