Semaglutide vs Liraglutide: Weight Loss, Evidence and Lab Results

The biggest difference between semaglutide and liraglutide is how much weight they took off in the two trials that compared them directly: semaglutide produced clearly more, in people with and without diabetes. Both are FDA-approved prescription drugs from Novo Nordisk that act on the same GLP-1 receptor, and both now have more than one brand name. Semaglutide is sold as Ozempic, Rybelsus and Wegovy; liraglutide as Victoza and Saxenda, with approved US generics. Liraglutide is the older, shorter-acting drug (first FDA-approved in 2010, versus 2017 for semaglutide), with its own large heart-outcomes trial, LEADER, in people with type 2 diabetes.

At a glance

How they work differently

They work in the same way at the receptor. Both bind and activate the GLP-1 receptor, which raises insulin release when blood sugar is high, lowers glucagon, slows stomach emptying and reduces appetite. The difference is the molecule around that receptor. Semaglutide's label describes a GLP-1 analogue with 94% sequence homology to human GLP-1, and says its long half-life comes mainly from binding to albumin in the blood, plus protection from the DPP-4 enzyme (DailyMed, Ozempic label, Novo Nordisk, June 2026). Liraglutide's label describes an acylated GLP-1 receptor agonist with 97% homology to human GLP-1(7-37), resistant to DPP-4 and NEP (DailyMed, Victoza label, Novo Nordisk).

The practical gap is how long each lingers. The labels give an elimination half-life of about one week for semaglutide and about 13 hours for liraglutide. That is the pharmacology behind semaglutide being the longer-acting drug. It is not a dosing guide, and this article does not give one.

What the evidence shows

Head-to-head: STEP 8, weight loss without diabetes

STEP 8 is the direct comparison for weight management. It randomized 338 adults with overweight or obesity and no diabetes to semaglutide or liraglutide, each at its own weight-management dose, or to placebo, for 68 weeks (a bit over a year). The average weight change was -15.8% with semaglutide and -6.4% with liraglutide, a difference of 9.4 percentage points. About 71% of the semaglutide group lost 10% or more of their body weight, against about 26% on liraglutide. More people stopped liraglutide for any reason (27.6% versus 13.5%), while gastrointestinal side effects were about equally common (84.1% and 82.7%) (Rubino et al., JAMA, 2022).

Two caveats from the paper itself. The comparison of the two drugs was open-label, so participants and staff knew which was which. And several authors were Novo Nordisk employees, which is normal for a company trial of its own products but worth knowing.

Head-to-head: SUSTAIN 10, type 2 diabetes

SUSTAIN 10 compared the two in 577 adults with type 2 diabetes who were already on oral diabetes drugs, for about seven months, again open-label. Average A1c fell by 1.7 percentage points with semaglutide and 1.0 with liraglutide, and weight fell by 5.8 kg versus 1.9 kg. Gastrointestinal side effects were more common with semaglutide (43.9% versus 38.3%), and so were stops because of side effects (11.4% versus 6.6%) (Capehorn et al., Diabetes & Metabolism, 2020). The trial authors chose the doses to reflect what is used in practice, so it shows how the two products compare as prescribed, not how the molecules compare amount for amount.

Where each has its own best evidence

Semaglutide's weight-loss case rests on STEP 1, which randomized 1,961 adults without diabetes to semaglutide or placebo: average weight change was -14.9% versus -2.4%, and half the semaglutide group lost 15% or more (Wilding et al., NEJM, 2021). Its current labels also cover heart-risk reduction and, for Ozempic, kidney outcomes in type 2 diabetes, and the Wegovy label carries a liver indication (MASH) that was granted under accelerated approval, meaning a confirmatory trial is still required (DailyMed, Wegovy label, Novo Nordisk, June 2026). For a fuller walk-through see our semaglutide guide.

Liraglutide's strongest evidence is cardiovascular. In LEADER, 9,340 people with type 2 diabetes and high heart risk were followed for a median of 3.8 years: heart death, heart attack or stroke occurred in 13.0% on liraglutide versus 14.9% on placebo (hazard ratio 0.87) (Marso et al., NEJM, 2016). Its weight-loss trial, SCALE, randomized 3,731 adults without diabetes for 56 weeks: 8.4 kg lost versus 2.8 kg on placebo (Pi-Sunyer et al., NEJM, 2015). See the liraglutide guide for the rest, including how the generics arrived.

Comparing numbers across separate trials, such as STEP 1 against SCALE, is unreliable: the populations, durations and designs differ. The two head-to-head trials above are the only fair comparison we found, and we opened both.

Who each label covers, and what has changed

The approvals overlap but are not identical. Wegovy is labeled for adults and for patients 12 and older with obesity, and now comes as a tablet as well as an injection. Saxenda is labeled for adults and for patients 12 and older who weigh more than 60 kg and have obesity, and Victoza for type 2 diabetes from age 10. Those details come straight from the current Novo Nordisk labels linked above and below. On the liraglutide side, the FDA approved the first generic of Victoza in December 2024 (FDA announcement), and Teva announced approval and launch of a generic Saxenda in August 2025 (Teva). For semaglutide, Apotex announced the first FDA tentative approval of a generic Ozempic-referencing injection on April 10, 2026; a tentative approval does not by itself allow the product to be marketed. Availability and pricing move quickly, so the current FDA and DailyMed listings are the place to confirm what exists today.

Side effects and risks compared

Very similar. Both drugs carry a boxed warning: they caused thyroid C-cell tumors in rodents, and whether they do in humans is unknown. Both are contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or the genetic syndrome MEN 2 (DailyMed, Wegovy; DailyMed, Saxenda, Novo Nordisk, June 2026). The everyday problems are gastrointestinal: nausea, vomiting, diarrhea and constipation, which is why so many people in these trials stopped treatment. The labels also warn about pancreatitis and gallbladder disease.

The trials say semaglutide's side-effect load was similar to liraglutide's in the weight-loss setting and somewhat heavier in the diabetes setting. A stronger drug is not automatically a riskier one, but neither is it automatically gentler. The labels for Wegovy and Saxenda both say that using the product with any other GLP-1 receptor agonist is not recommended.

All of this describes pharmacy-grade product made under inspection. It says nothing about what is in a vial sold as a research chemical.

What the lab tests show for each

Today, our database holds 18 semaglutide vials from 8 vendors, from 11 lab reports dated January 2025 through May 2026. 18 of the 18 with a purity result measured 99% pure or better (median 99.67%). The median amount came in 6.7% over the label, with 8 vials within 5% of label (15 were within 10% as of September 30, 2026), 0 more than 20% under and 0 more than 20% over. 0 of the 18 vials failed our definition (empty, under 95% pure, more than 20% under label or more than 50% over).

For liraglutide we have no lab results yet. We cannot say anything about purity or amount for vials sold as liraglutide, and we will not infer it from semaglutide.

That leaves a lopsided comparison. 18 vials is a small sample, and zero is no sample. Nothing here can rank the two compounds against each other, and even the semaglutide record could shift with a handful of new reports. Here is who has the strongest independent lab record for semaglutide right now:

Buying smarter

Start with the semaglutide results page and look at the number of reports behind any vendor's score and how recent they are. A vendor-posted certificate is a starting point, not proof; how to read a peptide COA and fake peptide COAs cover what to check. Since the liraglutide record is empty, testing your own vial is the only way to know what is in it. Underdosed peptides shows what wrong-amount vials look like in real reports. If a report comes back bad, stop using that batch, tell anyone who bought from the same run, take the report 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. Both drugs are FDA-approved prescriptions; vials sold as research peptides are unregulated products.