What is semaglutide? Benefits, evidence and what independent lab tests show

Semaglutide is a lab-made version of a gut hormone, GLP-1, that lowers blood sugar and reduces appetite. It's FDA-approved and sold under three brand names made by Novo Nordisk: Ozempic (an injection, now also a tablet) and the oral tablet Rybelsus for type 2 diabetes, and Wegovy (an injection, now also a tablet) for weight management and cardiovascular risk reduction. Most of what circulates on the research-peptide market under the name "semaglutide" is none of those — it's an unbranded, unapproved version sold "for research use only," which is what most of this article, and our database, actually covers.

What semaglutide is and how it works

Semaglutide is a modified version of GLP-1, a hormone your gut releases after eating. It binds to and activates GLP-1 receptors found in the pancreas, stomach, and brain: in the pancreas, it boosts insulin release and lowers glucagon (a hormone that raises blood sugar) when blood sugar is high; in the stomach, it slows how quickly food empties out; and in appetite-regulating regions of the brain, it reduces hunger signals (DailyMed, Ozempic prescribing information, Novo Nordisk; Wegovy prescribing information). It's sold as injectable Ozempic and Wegovy and as tablets: Rybelsus, plus tablet versions of Ozempic (DailyMed, Ozempic and Rybelsus tablets) and Wegovy.

The FDA first approved semaglutide in 2017, as Ozempic, to improve blood sugar control in adults with type 2 diabetes, later adding indications for reducing major cardiovascular events in those with established cardiovascular disease, and for reducing the risk of kidney function decline and cardiovascular death in those with chronic kidney disease. As Wegovy, the same active ingredient is approved for long-term weight management in adults and some adolescents with obesity (or overweight plus a weight-related condition), and separately to reduce cardiovascular risk in adults with established cardiovascular disease and obesity or overweight. The Wegovy injection is also approved, under accelerated approval, to treat noncirrhotic MASH (a fatty liver disease) with moderate to advanced liver fibrosis in adults. Buyers shorten it to "sema." It's the molecule that put GLP-1 drugs on the map before tirzepatide and retatrutide followed with additional receptor targets.

Semaglutide isn't a new idea chemically — it belongs to the same GLP-1 receptor agonist family as older drugs like liraglutide, modified to last far longer in the body than the older drugs. Gastrointestinal side effects were the main tolerability problem in its trials, as they were for tirzepatide and retatrutide; the side-effects section below covers what the labels report.

Why the brand names matter for buyers

As with tirzepatide, "semaglutide" isn't one single product — it's Ozempic, Rybelsus, and Wegovy, three FDA-approved products built on the same active ingredient but approved for different uses, at different doses, and in different forms (injections and tablets). A claim about semaglutide's weight-loss effect is really a claim about the Wegovy trials specifically; a claim about its diabetes effect points back to the Ozempic and Rybelsus program instead. Research-labeled semaglutide sold on the peptide market isn't any of these three regulated products — it's an unbranded version with none of their manufacturing oversight, sold under the same generic chemical name.

What people use it for

What the research actually shows

Weight loss in people without diabetes

The trial behind Wegovy's approval, STEP 1, randomly assigned 1,961 adults with obesity (or overweight plus a weight-related condition) who did not have diabetes to semaglutide or placebo, plus lifestyle counseling, for 68 weeks. At the dose studied, the average weight loss was 14.9%, compared with 2.4% on placebo — a difference of 12.4 percentage points. 86.4% of people on semaglutide lost 5% or more of their body weight (versus 31.5% on placebo), 69.1% lost 10% or more (versus 12.0%), and 50.5% lost 15% or more (versus 4.9%) (Wilding et al., NEJM 2021). Participants on semaglutide also saw bigger improvements in blood pressure, waist circumference, and self-reported physical function than those on placebo.

Head-to-head against tirzepatide in type 2 diabetes

SURPASS-2 compared semaglutide directly against tirzepatide in 1,879 people with type 2 diabetes already on metformin, over 40 weeks. Semaglutide, at the dose used in that trial, reduced A1c by an average of 1.86 percentage points and body weight by 5.7 kilograms; every tirzepatide dose tested beat that on both measures, with the largest gap at the highest tirzepatide dose studied (Frías et al., NEJM 2021). That doesn't make semaglutide's own result small — a 1.86-point A1c drop and meaningful weight loss are both clinically significant — it's simply the most direct comparison in people with type 2 diabetes, and it came out in tirzepatide's favor in this specific trial.

Head-to-head against tirzepatide in obesity

SURMOUNT-5 randomly assigned 751 adults with obesity but without type 2 diabetes to tirzepatide or semaglutide, each at the highest dose a person could tolerate, for 72 weeks. Average weight loss was 20.2% on tirzepatide versus 13.7% on semaglutide (Aronne et al., NEJM 2025). The trial was open-label and funded by Eli Lilly, which makes tirzepatide, so read it with that in mind.

Cardiovascular and kidney outcomes

Beyond weight and blood sugar, semaglutide's label includes indications tied to outcomes trials showing reduced cardiovascular events in people with existing cardiovascular disease, and reduced kidney-disease progression in people with type 2 diabetes and chronic kidney disease. Those are separate, dedicated outcome trials beyond the weight-loss and glycemic studies described above, and they're the basis for the broader indications on Ozempic and Wegovy's current labels (DailyMed, Ozempic label; Wegovy label).

How semaglutide's diabetes trials shaped the weight-loss trials that followed

Before Wegovy existed, semaglutide had already been studied for years in people with type 2 diabetes under the SUSTAIN trial program, at doses approved for glycemic control. Those earlier trials consistently showed some weight loss as a side effect of treating diabetes, which is part of what motivated Novo Nordisk to run a dedicated, higher-dose weight-management program (STEP) in people without diabetes. That sequence — diabetes drug shows weight-loss signal, company runs dedicated obesity trials at a higher dose — is the same path tirzepatide later followed from Mounjaro to Zepbound, and it's worth knowing because it explains why the weight-loss dose used in STEP 1 and Wegovy is higher than the ceiling dose approved for Ozempic.

Side effects and risks

Semaglutide's FDA labels carry the same boxed warning as tirzepatide's: in rodents, semaglutide causes thyroid C-cell tumors, and it's unknown whether it does the same in humans. Both Ozempic and Wegovy are contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. In the STEP 1 trial, the most common side effects were gastrointestinal — nausea, diarrhea, vomiting, and constipation — reported by 74.2% of the semaglutide group versus 47.9% on placebo, mostly mild-to-moderate and resolving without stopping treatment. Gallbladder-related disorders (mostly gallstones) were reported in 2.6% of the semaglutide group versus 1.2% on placebo, and mild acute pancreatitis occurred in three participants on semaglutide, all of whom recovered.

That's the safety picture for the regulated product, manufactured in an inspected facility with release testing on every batch. Research-labeled semaglutide sold outside that system doesn't come with any of that oversight — no guarantee of what's actually in the vial, at what purity, or at what amount relative to the label.

What the lab tests show

As of September 30, 2026, our database includes 18 semaglutide vials from 8 vendors, drawn from 11 lab reports, dated January 2025 through May 2026. This is a much smaller sample than tirzepatide's or retatrutide's — worth keeping in mind, since a single vendor or a handful of new reports could shift these numbers more than they would for a deeper-tested compound. As of September 29, 2026, the results were strikingly clean: all 18 vials came in at 99% purity or higher, with a median of 99.67%.

Dose against label was similarly tight as of September 29, 2026, for a market that often runs hot: the median result was +6.7% over label, with 8 of the 18 vials landing within ±5% of label and 15 of 18 within ±10%. None measured more than 20% under or over label. No vial in our semaglutide data failed under our scoring rules (empty, under 95% pure, more than 20% under label, or more than 50% over) — a 0% failure rate, though on a sample this size that reflects the vials that happened to get tested and reported, not a guarantee about the wider market.

We don't yet have enough endotoxin, sterility, or other add-on test results specific to semaglutide to say anything reliable about them — those tests are ordered separately from the core purity and quantity panel, and buyers haven't ordered many for this compound yet in our data. That's a real gap, not a clean bill of health; it just means the question hasn't been asked enough times yet to answer.

Ranking requires five or more lab reports on a specific compound, and semaglutide's vendor sample is still thin enough that this may be short or empty. Here's the live picture, which updates as new reports come in:

Check the semaglutide results page for the current, continuously updated numbers — they'll move faster than this article as more reports come in, given how small the current sample is.

What the data can't tell you

A lab report can confirm what's in a specific vial, at what purity and what amount relative to the label — that's genuinely useful, and it's more than most buyers have without one. It can't tell you whether the next vial from the same vendor will look the same, whether a vial was handled or stored correctly before you received it, or anything about a vendor's communication, shipping, or refund practices. With a sample this small for semaglutide specifically, it also can't tell you much about the wider market yet; a sample this size is enough to notice a pattern, not enough to call it settled. That's a real limitation worth naming rather than glossing over, especially for a compound whose approved version is this well studied.

Buying smarter

With only 18 vials logged as of September 29, 2026, semaglutide was one of the thinner records in our database, so don't treat a vendor's clean results here as a settled verdict — check /peptides/semaglutide for the latest count before leaning on it. The same baseline checks apply regardless of sample size: learn to read a peptide COA and watch for fake-COA patterns before trusting anything a vendor posts, since a posted certificate isn't the same as an independent, buyer-commissioned report. Given how little endotoxin and sterility data exists for semaglutide specifically, testing your own vial does more to grow the record here than for a heavily tested compound. If a report comes back bad, stop using that batch, tell anyone who bought from the same run, bring it to the vendor, and submit it to VendorVerify.

Database figures without a date update automatically from VendorVerify's lab results; dated figures are snapshots. This isn't medical advice, and research-labeled semaglutide is sold for research use only.