Semaglutide: what it is, side effects, dosing and the research

Semaglutide is a synthetic analogue of glucagon-like peptide-1 (GLP-1), a gut hormone released after eating. Natural GLP-1 is broken down within minutes. Novo Nordisk’s chemists extended its life by swapping two amino acids (Aib at position 8 and arginine at position 34) and attaching a fatty-acid side chain at lysine 26, which binds the peptide to albumin in the blood; the 2015 discovery paper describes how this was designed to allow once-weekly dosing ^[1].

It is sold as three branded medicines: Ozempic (weekly injection for type 2 diabetes), Rybelsus (daily tablet for type 2 diabetes) and Wegovy (weekly injection, and since December 2025 in the US a daily tablet, for weight management) ^[11]. These are made under pharmaceutical manufacturing standards, supplied in fixed-dose pens or tablets, and prescribed by a clinician.

Semaglutide is also widely offered by online vendors as a freeze-dried powder labelled “for research use only”. That product is not Ozempic or Wegovy. It is made by unknown manufacturers, is not batch-released by a regulator, and its identity and dose can only be checked by independent testing. Our guide to what research peptides are explains why the label matters. Semaglutide is often compared with the dual agonist tirzepatide and the investigational triple agonist retatrutide.

Yes. Ozempic, Wegovy and Rybelsus all contain semaglutide, so a search for the semaglutide brand name usually leads to one of these three. What differs between them is the approved use, the dose range and the form. Ozempic injection is approved in the US for type 2 diabetes, including to lower the risk of major cardiovascular events and of kidney decline in people with type 2 diabetes and chronic kidney disease ^[14]. Wegovy is approved for weight reduction and long-term weight maintenance, for cardiovascular risk reduction in adults with established heart disease and obesity or overweight, and, as an injection, for a form of fatty liver disease with fibrosis called MASH ^[13].

The US label now also covers semaglutide tablets under two names, Rybelsus and Ozempic tablets, both for type 2 diabetes. The label states that the two tablet products are not substitutable milligram for milligram ^[15]. Wegovy tablets are a separate, higher-dose tablet for weight management ^[13].

Zepbound and Mounjaro are not semaglutide. Both contain tirzepatide, a different molecule that acts on GIP as well as GLP-1 receptors ^[22]. Liraglutide (Saxenda, Victoza) is an older, daily GLP-1 drug, compared with semaglutide below.

Semaglutide activates the GLP-1 receptor, which is found in the pancreas, the gut and the brain. In the pancreas this increases insulin release and reduces glucagon release when blood glucose is raised, which is why it lowers blood sugar in type 2 diabetes. It also slows stomach emptying and acts on appetite centres in the brain, reducing hunger and food intake; this appetite effect is the main driver of the weight loss seen in trials.

The albumin binding described in the discovery paper is what gives semaglutide its long half-life ^[1]. In people, the half-life of semaglutide 2.4 mg was measured at about 145 to 165 hours, roughly a week, which allows a single weekly injection ^[12]. The weight-management dose (2.4 mg weekly) is higher than the doses used in the diabetes outcome trials described below (0.5 mg or 1.0 mg weekly).

The Wegovy label summarises the pharmacology this way: semaglutide decreases calorie intake, probably by affecting appetite, and lowers body weight with more loss of fat mass than lean mass. It notes that the GLP-1 receptor is present in several brain areas involved in appetite regulation ^[13].

The pivotal obesity trial, STEP 1, enrolled 1,961 adults with a BMI of 30 or more (or 27 or more with a weight-related condition) who did not have diabetes. Over 68 weeks, participants on semaglutide 2.4 mg once weekly plus lifestyle advice lost an average of 14.9% of body weight, against 2.4% on placebo; about half of the semaglutide group lost 15% or more ^[2].

STEP 4 asked what happens when treatment stops. After everyone took semaglutide for a 20-week run-in (losing an average of 10.6%), 803 participants were randomised to continue or switch to placebo. Over the next 48 weeks, those who continued lost a further 7.9%, while those switched to placebo regained 6.9% ^[3]. This is the main trial evidence that weight tends to return after stopping.

In a head-to-head trial in adults with obesity but without diabetes (SURMOUNT-5), tirzepatide at its maximum tolerated dose produced greater weight loss at 72 weeks than semaglutide at its maximum tolerated dose: 20.2% against 13.7% ^[8].

A higher weekly dose, 7.2 mg, was tested in two 72-week trials described on the US label. In adults with obesity and no diabetes, average weight change was −18.8% on 7.2 mg, −15.5% on 2.4 mg and −3.9% on placebo. In adults with obesity and type 2 diabetes the figures were −13.2%, −10.4% and −3.8% ^[13]. People with type 2 diabetes lost less weight than people without it in both the 2.4 mg and 7.2 mg trials, a pattern seen across GLP-1 drugs.

In these trials semaglutide was always given alongside a reduced-calorie diet (about 500 kcal a day below requirements) and advice to do at least 150 minutes of physical activity a week ^[13]. The trials did not test a particular diet, so they do not answer what to eat on semaglutide beyond that general calorie deficit.

STEP 8 is the only randomised trial to compare the two GLP-1 drugs licensed for weight management directly. It enrolled 338 adults with overweight or obesity and no diabetes and gave them weekly semaglutide 2.4 mg or daily liraglutide 3.0 mg, each against a matching placebo, for 68 weeks ^[16].

Average weight change was −15.8% with semaglutide and −6.4% with liraglutide (−1.9% with placebo). A loss of 10% or more was reached by 70.9% on semaglutide and 25.6% on liraglutide. Gastrointestinal side effects were similar (84.1% and 82.7%), but fewer people stopped semaglutide than liraglutide for any reason (13.5% against 27.6%) ^[16]. The comparison was open-label between the two active drugs, which is a limitation.

Tirzepatide vs semaglutide is the most searched comparison in this class, and two randomised trials have tested it directly. The difference between semaglutide and tirzepatide starts with the receptors: semaglutide acts only at the GLP-1 receptor, while tirzepatide also activates the GIP receptor ^[22]. Our Tirzepatide vs semaglutide comparison sets the two side by side.

In SURMOUNT-5, 751 adults with obesity and no diabetes were randomised to the maximum tolerated dose of either drug. Over 72 weeks weight fell by 20.2% with tirzepatide and 13.7% with semaglutide ^[8]. In SURPASS-2, in type 2 diabetes, semaglutide 1 mg lowered HbA1c by 1.86 percentage points over 40 weeks, and all three tirzepatide doses lowered it further; rates of nausea were similar in the two groups ^[7].

These results say which drug produced more weight loss on average in those populations. They do not decide the right medicine for an individual, which depends on other conditions, tolerability, cost and availability, and is a prescriber’s decision. Switching from semaglutide to tirzepatide has not been tested as a protocol in these trials. The UK regulator advises that people speak to a healthcare professional before switching between any GLP-1 medicines, including between brands of the same drug, because the medicines differ in strength and use ^[21].

Retatrutide vs semaglutide is also searched, but retatrutide is an unapproved, investigational drug and has not been compared with semaglutide in a published head-to-head trial. See our retatrutide guide for its trial results.

SUSTAIN-6 tested semaglutide 0.5 mg or 1.0 mg weekly in 3,297 people with type 2 diabetes at high cardiovascular risk. Over 104 weeks, the combined rate of cardiovascular death, non-fatal heart attack or non-fatal stroke was 6.6% with semaglutide and 8.9% with placebo. The same trial found more diabetic eye (retinopathy) complications in the semaglutide group ^[4].

SELECT extended this to people without diabetes. It enrolled 17,604 adults aged 45 or over with existing cardiovascular disease and a BMI of 27 or more. Over a mean follow-up of about 40 months, major cardiovascular events occurred in 6.5% on semaglutide 2.4 mg against 8.0% on placebo, a 20% relative reduction ^[5].

FLOW studied semaglutide 1.0 mg weekly in 3,533 people with type 2 diabetes and chronic kidney disease. The trial was stopped early for efficacy: the risk of major kidney disease events was 24% lower with semaglutide, and death from any cause was 20% lower ^[6].

In type 2 diabetes, the SURPASS-2 trial compared semaglutide 1 mg with tirzepatide. Semaglutide lowered HbA1c by 1.86 percentage points over 40 weeks; all three tirzepatide doses lowered it further ^[7].

Interest in semaglutide’s impact on drinking comes from animal and observational data suggesting GLP-1 drugs may reduce alcohol intake. The first randomised test was a small phase 2 trial of 48 adults with alcohol use disorder who were not seeking treatment. Over 9 weeks of low-dose semaglutide (0.25 mg rising to 0.5 mg, then one 1.0 mg dose) or placebo, semaglutide reduced the amount of alcohol drunk in a laboratory drinking session, drinks per drinking day and craving, but did not change average drinks per day or the number of drinking days ^[18].

The authors described this as initial evidence that justifies larger trials, not as proof of a treatment effect. Alcohol use disorder is not an approved use of semaglutide, and the labels do not set out specific advice on drinking alcohol while taking it.

Unlike most peptides covered on this site, semaglutide has been studied in tens of thousands of people in randomised, placebo-controlled trials published in journals such as the New England Journal of Medicine and JAMA. The trials above are a small selection. The evidence applies to the licensed products used at the licensed doses under medical supervision; it does not tell you anything about the content or purity of an unlicensed vial bought online.

Blood levels build up gradually. With once-weekly injections, steady-state exposure is reached after 4 to 5 weeks ^[14]. The Wegovy injection schedule then takes 16 weeks to step up to the 2.4 mg maintenance dose ^[13], so the first months of treatment are at lower doses.

The trial timepoints show how semaglutide weight loss built up over time. In the STEP 4 run-in, participants had lost an average of 10.6% after 20 weeks ^[3]. In STEP 1 the average was 14.9% at 68 weeks ^[2], and in the 7.2 mg trials 18.8% at 72 weeks ^[13]. Blood-glucose effects in diabetes trials were measured earlier, for example at 40 weeks in SURPASS-2 ^[7].

Responses vary widely between people. In STEP 8, about 71% of people on semaglutide lost 10% or more of their weight, which means nearly three in ten did not reach that level ^[16]. People with type 2 diabetes lost less on average than people without it ^[13]. These are trial averages, not a prediction for any individual.

Semaglutide is the only GLP-1 peptide that has been made to work as a tablet. The tablets contain an absorption enhancer, salcaprozate sodium (SNAC), and absorption happens mainly in the stomach. Even so, only about 0.4% to 1% of a Rybelsus dose and 1% to 2% of an Ozempic tablet dose reaches the bloodstream, which is why tablet doses are measured in several milligrams a day while injections are under a few milligrams a week ^[15].

Because absorption is so sensitive to food and drink, the label instructs that semaglutide tablets are taken on an empty stomach in the morning with up to 4 ounces (about 120 mL) of water, swallowed whole, with a wait of at least 30 minutes before eating, drinking or taking other oral medicines ^[15].

For weight management, oral semaglutide was tested in OASIS 4: 307 adults with overweight or obesity and no diabetes took 25 mg daily or placebo. Average weight change at 64 weeks was −13.6% with the tablet and −2.2% with placebo; gastrointestinal side effects affected 74.0% on semaglutide and 42.2% on placebo ^[17]. This is the trial behind the Wegovy tablet. For comparison, the injection produced 14.9% at 68 weeks in STEP 1 ^[2], but those are different trials and not a head-to-head comparison.

The US Wegovy label allows switching between forms: a person on the 2.4 mg injection may start 25 mg tablets one week after the last injection, and someone on 25 mg tablets may start the 2.4 mg injection the day after the last tablet ^[13]. Oral semaglutide for weight loss in non-diabetics therefore now has a labelled product in the US; in the UK, the MHRA lists Rybelsus as licensed for diabetes, not weight management ^[21].

The STEP obesity trials used 2.4 mg by subcutaneous injection once weekly, reached by gradual dose escalation (in STEP 4 the escalation took 16 weeks) ^{[2] [3]}. SELECT also used 2.4 mg weekly ^[5]. The diabetes outcome trials used lower weekly doses: 0.5 mg or 1.0 mg in SUSTAIN-6 and 1.0 mg in FLOW ^{[4] [6]}.

These are the doses studied in trials of the licensed medicine, reported here for information only. They are not a recommendation, and they cannot be transferred to research powders whose actual peptide content is unknown. Our peptide calculator explains reconstitution arithmetic but cannot correct for a mislabelled vial.

People searching for a semaglutide dosing chart are usually looking for the escalation schedule printed on the prescribing information. For Wegovy injection, the US label sets a starting dose of 0.25 mg once weekly for weeks 1 to 4, then 0.5 mg for weeks 5 to 8, 1 mg for weeks 9 to 12 and 1.7 mg for weeks 13 to 16. The maintenance dose for weight reduction is 1.7 mg or 2.4 mg weekly, and for people who have tolerated 2.4 mg for at least 4 weeks the label allows a maximum of 7.2 mg weekly. The stated purpose of the slow escalation is to reduce gastrointestinal side effects ^[13].

Ozempic starts the same way, at 0.25 mg weekly for 4 weeks and then 0.5 mg, with possible steps to 1 mg and a maximum of 2 mg weekly for blood-glucose control ^[14]. Wegovy tablets start at 1.5 mg a day for 30 days, then 4 mg and 9 mg, reaching the 25 mg maintenance dose from day 91 ^[13]. Rybelsus starts at 3 mg a day for 30 days, then 7 mg, with 14 mg if needed ^[15]. So the highest dose of semaglutide on any US label is 7.2 mg weekly by injection or 25 mg daily by tablet.

The labels describe the injection as given under the skin of the abdomen, thigh or upper arm, on the same day each week at any time of day, with the site rotated each time ^[13]. For a missed Wegovy injection, the label says to take it if the next dose is more than 2 days away and to skip it if it is less than 2 days away; if two or more doses in a row are missed, escalation is restarted at a lower dose ^[13]. The Ozempic label uses a 5-day window instead ^[14].

Semaglutide dosage in units is a question about compounded or research vials, because licensed pens are dialled in milligrams. On a standard U-100 insulin syringe, 100 units equal 1 mL, so the number of milligrams in a given number of units depends entirely on the concentration in the vial. At 2.5 mg per mL, for example, 20 units (0.2 mL) hold 0.5 mg and 40 units (0.4 mL) hold 1 mg; at a different concentration the same units hold a different amount. The FDA has received reports of adverse events, some needing hospital care, linked to people measuring the wrong dose of compounded semaglutide and to clinicians miscalculating doses ^[19]. The peptide calculator shows the arithmetic.

Microdosing semaglutide, meaning regular use of doses below the labelled schedule, has not been tested in any randomised trial we could find. The 0.25 mg dose on the labels is a starting step within an escalation schedule, not a studied maintenance regimen ^[13].

The most common side effects in trials were gastrointestinal: nausea, diarrhoea, vomiting and constipation. In STEP 1 these were usually mild to moderate and eased over time, but 4.5% of semaglutide users stopped treatment because of gastrointestinal events, against 0.8% on placebo ^[2]. In SELECT, 16.6% on semaglutide and 8.2% on placebo permanently stopped the study drug because of adverse events ^[5].

SUSTAIN-6 found a higher rate of diabetic retinopathy complications with semaglutide (hazard ratio 1.76) in people with type 2 diabetes ^[4]. Prescribing information for GLP-1 medicines also warns about pancreatitis, gallbladder problems and, in the US, carries a boxed warning about thyroid C-cell tumours seen in rodents. Anyone taking the licensed medicine should follow their prescriber’s advice.

Unlicensed products add further risks. A 2024 study that bought semaglutide from illegal online pharmacies found that all three vials delivered were probably substandard or falsified: measured purity was only 7.7% to 14.4% against a claimed 99%, and bacterial endotoxin was detected in every sample. None of the three Ozempic pens ordered arrived ^[9].

The US Wegovy label pools three placebo-controlled weight trials of the 2.4 mg injection. Compared with placebo, the rates were: nausea 44% against 16%, diarrhoea 30% against 16%, vomiting 24% against 6%, constipation 24% against 11%, abdominal pain 20% against 10%, headache 14% against 10% and fatigue 11% against 5% ^[13]. So the answer to whether semaglutide makes you tired is that fatigue was reported about twice as often as on placebo, in roughly one person in ten.

Does semaglutide cause hair loss? In the same pooled trials, hair loss was reported by 3.3% on semaglutide 2.4 mg (4% of women and 0.9% of men) against 1% on placebo, and the label links these reports to weight reduction. On the 7.2 mg dose hair loss was reported by 5.8% ^[13]. The 7.2 mg dose also caused more dysaesthesia (altered skin sensation such as tingling or burning): 22%, against 6% on 2.4 mg ^[13].

Gallstones were more common on semaglutide injection (1.6% against 0.7% on placebo), and the label notes this excess remained after accounting for the amount of weight lost ^[13]. The MHRA has strengthened warnings on acute pancreatitis, including rare serious or fatal cases, for GLP-1 medicines, and has reported very rare cases of a serious eye condition, non-arteritic anterior ischaemic optic neuropathy (NAION), linked to semaglutide ^[21].

On cancer, the evidence is from animals. Semaglutide causes thyroid C-cell tumours in rodents, and the label states it is unknown whether it causes thyroid tumours, including medullary thyroid carcinoma, in humans. Semaglutide is contraindicated in people with a personal or family history of medullary thyroid carcinoma or with MEN 2 syndrome ^[13].

How long do semaglutide side effects last? In the trials, gastrointestinal effects were concentrated during dose escalation and usually eased over time ^[2]. There is no recognised withdrawal syndrome on the labels; the main documented effect of stopping is weight regain, as in STEP 4 ^[3]. The Wegovy label advises stopping at least 2 months before a planned pregnancy because of the long half-life ^[13].

Compounded semaglutide is semaglutide prepared by a pharmacy or outsourcing facility rather than made by Novo Nordisk. In the US, compounding copies of a commercial drug is allowed only in limited circumstances, and it expanded while semaglutide injection was on the FDA’s shortage list. The FDA declared that shortage resolved on 21 February 2025, and the period during which it did not intend to act against state-licensed pharmacies making copies ended on 22 April 2025 ^[20].

The FDA states that compounded drugs are not FDA approved and are not reviewed for safety, effectiveness or quality before they are sold ^[19]. It has warned that some compounders use salt forms, semaglutide sodium and semaglutide acetate, which are different active ingredients from the one in the approved drugs, and that it knows of no lawful basis for using them in compounding ^[19]. As of 31 May 2026 the FDA had received 990 reports of adverse events associated with compounded semaglutide, while noting that such reports are likely to be under-reported ^[19].

Compounded semaglutide with B12 (cyanocobalamin) is a common product in the US. The FDA uses exactly this combination as an example: it may consider a compounded injection of semaglutide plus B12 to be essentially a copy of commercially available products when the amounts of each are within 10% of an approved strength and the route is the same ^[20]. No approved semaglutide medicine contains B12.

Does compounded semaglutide work? No randomised trial has tested a compounded product, so the trial results on this page cannot be assumed to apply to it. In the UK the position is simpler: the MHRA states that legitimate GLP-1 medicines come as prefilled pens or tablets, and that products supplied as a powder in vials to be mixed before injection are not authorised ^[21].

Semaglutide is an approved prescription-only medicine. In the US it is licensed as Ozempic and Rybelsus for type 2 diabetes and Wegovy for chronic weight management; the FDA approved the oral Wegovy tablet in December 2025 ^[11]. It is also licensed in the UK, the EU and many other countries. Licensed use requires a prescription; buying unlicensed “research” semaglutide for personal injection is a different matter, and the rules on sale and possession vary by country, as set out on our legal status pages.

In the UK, the MHRA lists semaglutide as licensed for weight management as Wegovy and for diabetes as Ozempic and Rybelsus. All GLP-1 medicines are prescription-only. Some are available on the NHS, with availability depending on location and on whether treatment is for diabetes or weight loss, and they can also be obtained privately after a consultation with a prescriber. The MHRA says selling them through unregulated channels such as beauty salons or social media is against the law ^[21]. Our UK legal status page covers unlicensed products.

In the US, the FDA has warned companies selling semaglutide falsely labelled “for research purposes” or “not for human consumption” and urges consumers not to buy such products ^[19]; see the US legal status page.

WADA added semaglutide to its Monitoring Program in 2024, which tracks use of a substance in sport ^[10]. Athletes should check the current Prohibited List and their national anti-doping organisation rather than rely on third-party summaries.

Licensed semaglutide pens are kept in a refrigerator before first use and must not be frozen; the patient leaflet for each product sets out how long it can then be kept at room temperature. Research-grade semaglutide is usually a freeze-dried powder, which is generally kept cold, dry and away from light, and refrigerated once reconstituted. See our guides to storing peptides and bacteriostatic water.

The US labels give the details. Wegovy single-dose pens are stored at 2 °C to 8 °C and, if needed, can be kept between 8 °C and 30 °C for up to 28 days before the cap is removed; they must be protected from light. The multi-dose Wegovy FlexTouch pen and the Ozempic pen can be used for 56 days after first use, either at room temperature (15 °C to 30 °C) or in a refrigerator ^{[13] [14]}. Does semaglutide expire? Each pen carries an expiry date, and these in-use periods are the limits once it is out of the fridge or opened.

How long does semaglutide stay in your system? With an elimination half-life of about one week, the label states that semaglutide remains in the circulation for about 5 to 7 weeks after the last 2.4 mg or 7.2 mg injection or 25 mg tablet ^[13]. This long tail is why the pregnancy advice above allows a 2-month gap.

PepFinder does not sell semaglutide. If you are comparing research suppliers, you can compare prices, learn how to read a COA, and see which vendors publish third-party tested batches. Given the purity results above, an independent certificate that confirms identity and content is the minimum to look for.

Listings for semaglutide UK prices are for research-labelled material, which the MHRA says is not an authorised medicine in that form ^[21]. Our guides to third-party peptide testing and spotting a fake peptide supplier explain what a genuine test report looks like.