What is semaglutide? Approved uses, evidence, and what the grey market actually sells

What semaglutide is

You've almost certainly met this molecule under a brand name before you met it under its own. Wegovy, Ozempic, Rybelsus.

All three contain semaglutide.

It's a GLP-1 receptor agonist, which means it mimics a hormone your gut already releases after you eat. That hormone tells your pancreas to release insulin, tells your brain you've had enough, and slows how fast your stomach empties.²

Semaglutide does the same job, more strongly and for far longer than the natural version lasts.

Our profile spells out the mechanism: it activates the GLP-1 receptor, raises insulin release when glucose is present, lowers glucagon, cuts appetite and food intake, and slows the stomach.

That last one is why the side effects are mostly digestive.

It's also a peptide, which is worth saying plainly because the word gets used to imply something exotic. Semaglutide is a chain of amino acids with a chemical modification that keeps it in the bloodstream for about a week. Nothing about being a peptide makes it unusual as a drug.

What it's actually approved for

Semaglutide is FDA approved, and the approvals are narrower than the conversation around it.

Each product is its own approval, with its own indication and formulation.¹

So Wegovy, Ozempic, and Rybelsus aren't three names for one interchangeable thing. A clinician choosing between them is making a real decision, not a branding one.

Here's the part people most often get wrong. An approval attaches to a specific finished product, for a specific named use.

A compound sold "for research" inherits none of it. The chemistry can look identical on paper and it still doesn't carry over.³

Our semaglutide profile tracks the regulatory detail and the graded outcomes with their sources.

How good is the evidence?

Strong, and unusually so for something in the peptide conversation.

We rate it high evidence with an established record, which only four compounds in our research directory currently earn. Large randomized trials support clinically meaningful weight reduction.

There's also cardiovascular outcome data, which matters more than weight data and is much rarer. In adults with established cardiovascular disease and overweight or obesity without diabetes, the SELECT trial found fewer major cardiovascular events.

Read that sentence carefully, because the qualifiers are the substance. Established cardiovascular disease, overweight or obesity, without diabetes. That's who was studied, and a finding applies to the population it was measured in.

Results differ by product and formulation too. So "semaglutide cuts heart attacks" is a compression that drops the part making it true.

The grey-market problem: there's almost nothing to check

Here's where our own data says something you won't find on a vendor page.

We maintain a testing ledger of 117 published lab records covering 11 compounds, each traceable to the original laboratory document.⁴

Exactly 2 of those 117 records are semaglutide.

Ledger as of the records published to date; vendor counts from our price market, checked 25 July 2026.

Two records is not a sample you can draw conclusions from. That is the finding.

For most compounds we can say something about how the supply behaves. For semaglutide sold outside a pharmacy, there's almost no published data at all.

And missing data is not a clean bill of health. It's a blank.

Both records we do have measured above their labelled dose. One 10mg vial came back at 10.68mg, and another at 11.9mg, which is 18.9% over. Purity on both was above 99.4%.

Two samples. Draw nothing from it beyond the obvious: nobody is checking this.

What a price comparison does and doesn't tell you

Semaglutide runs $45.00 to $125.00 across the two research vendors listing it, as of our 25 July 2026 check.

That's a narrow range by peptide standards, and it's narrow because two listings can't produce a wide one. It isn't evidence of price discipline.

These are also package prices for material that isn't authorized for human use. That puts them in a different category from a prescription entirely.

We keep prescription pricing in its own table for that reason, and we've written up why weight-care prices resist honest comparison.

Where semaglutide sits

Two things are true at once, and holding both is the whole skill.

The molecule has excellent evidence behind it. Better than almost anything else discussed as a peptide, including outcome data most compounds will never generate.

The supply outside a pharmacy is nearly unverifiable. Two lab records across our entire ledger, and no way to check what shipped.

Strong evidence for a molecule is not evidence about a vial. Those are separate questions, and the second one is the one a purchase actually turns on.

For the dual-agonist next to it on every vendor page, see what tirzepatide is, or read the two side by side. If you're starting from scratch, what peptides actually are is the better first stop.