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Semaglutide dosage, how it is taken and side effects: Wegovy, Ozempic and the UK licence
Semaglutide is licensed in the UK as Ozempic (type 2 diabetes) and Wegovy (weight management). The dosing schedules each licence sets, how the weekly injection is taken, the STEP 1 trial results, the side effects recorded, how access works, and why unlicensed "research" semaglutide is a different thing.
Semaglutide is the molecule in Ozempic and Wegovy, two licensed once-weekly injections that share a schedule of starting low and stepping up every four weeks. For type 2 diabetes the maintenance dose is 0.5 mg to 2 mg a week; for weight management it is 2.4 mg a week, reached after sixteen weeks of escalation. In the main weight trial, people on 2.4 mg lost on average about 15% of their body weight over 68 weeks, with gut side effects the main reason people struggled. This article explains where each number comes from, how the drug is taken, what the side-effect record shows, how access works, and why a vial sold online as "research semaglutide" is not the same thing as either medicine. It describes a licensed medicine; it does not recommend one. That decision belongs with a prescriber.
One molecule, two licences
Semaglutide mimics GLP-1, a hormone released from the gut after eating that slows stomach emptying, increases insulin release when blood sugar is high, and acts on appetite centres in the brain. It was developed by Novo Nordisk and licensed first for type 2 diabetes as Ozempic, then, at a higher dose, for weight management as Wegovy. An oral tablet, Rybelsus, is licensed for diabetes. The injectable products are the same drug in different pens at different strengths, which is why the dosing conversation depends entirely on which licence is being discussed.
The licensed dosing schedules
Both injectable licences use a slow escalation. The schedule is fixed in the product information and the prescriber decides where to hold.
- Wegovy (weight management): 0.25 mg once weekly for four weeks, then 0.5 mg for four weeks, then 1 mg for four weeks, then 1.7 mg for four weeks, then 2.4 mg once weekly as the maintenance dose. The first four steps are for tolerance; 2.4 mg is the dose the trials studied. If a step is not tolerated, the escalation can be delayed by four weeks.
- Ozempic (type 2 diabetes): 0.25 mg once weekly for four weeks, then 0.5 mg once weekly. If more blood-sugar control is needed after at least four weeks, 1 mg once weekly, and after a further four weeks, 2 mg once weekly as the maximum.
The slow start is not caution for its own sake. The gastrointestinal side effects are dose-related and peak when the dose rises, and the trials that established the schedule found that four-week steps kept most people comfortable enough to continue. Doses are fixed amounts for everyone, not adjusted for body weight, and the prescriber decides on the maintenance dose and any pauses in escalation.
How semaglutide is taken
The licence describes administration as once a week, on the same day each week, by injection into the fatty tissue under the skin of the abdomen, thigh or the back of the upper arm, rotating the site. Wegovy is supplied as fixed-dose pre-filled pens, each holding four weekly doses of one strength; Ozempic as multi-dose pens with the dose dialled before each injection. It can be taken at any time of day, with or without food. A pharmacist or clinician demonstrates the pen and the patient is reviewed as the dose increases.
The licensed information covers the practical questions that generate most searches. The product information states that a missed Wegovy dose can be taken within five days; after that it is skipped and the next dose taken on the usual day. Pens are stored in a fridge before first use and can be kept at room temperature, below 30°C, for a limited period once in use. Rybelsus tablets are taken daily on an empty stomach with a small amount of water, at least 30 minutes before food, drink or other medicines, because food reduces how much is absorbed. The patient leaflet, which comes with every pack, is written for exactly these questions and is the authority on them.
Weight loss in the STEP 1 trial
The trial behind the Wegovy licence is STEP 1, published in the New England Journal of Medicine in 2021. It enrolled 1,961 adults with a body-mass index of 30 or more, or 27 or more with at least one weight-related condition, without diabetes, and randomised them to semaglutide 2.4 mg weekly or placebo for 68 weeks, both alongside diet and activity support. Average weight change was about 14.9% on semaglutide against about 2.4% on placebo. Around 86% of those on semaglutide lost at least 5% of their body weight, and around a third lost 20% or more.
Companion trials in the STEP programme studied people with diabetes, compared semaglutide with lifestyle intervention alone, and followed what happened when the drug was stopped: a large part of the lost weight returned over the following year. That last finding is why the licence treats semaglutide as an ongoing treatment rather than a course, and it is the honest caveat to every headline figure. The averages describe a monitored trial with lifestyle support; individual results ranged widely; and the effect depends on continuing.
Side effects recorded in the trials and on the licence
The dominant side effects are gastrointestinal: nausea, diarrhoea, vomiting, constipation and abdominal pain. In STEP 1 they were mostly mild to moderate, most frequent during escalation, and a small proportion of participants stopped because of them. The licence lists less common but more serious risks: gallbladder disease including gallstones, which is more likely with rapid weight loss; acute pancreatitis; low blood sugar when combined with insulin or a sulfonylurea; and, in people with diabetic eye disease, worsening of retinopathy, which is monitored. Because the drug slows stomach emptying, it can alter how other medicines are absorbed.
These are the reasons the drug is prescribed and reviewed rather than sold off a shelf, and they are also the reasons the side-effect figures from the trials cannot be transferred to an unlicensed product. Trial data describe pharmaceutical semaglutide at a known dose. A vial of unknown content has no such data.
How access works in the UK
Semaglutide is a prescription-only medicine. Ozempic is prescribed for type 2 diabetes through GPs and diabetes services. For weight management, NICE recommended Wegovy in March 2023 for adults meeting body-mass index and weight-related condition thresholds, through specialist weight-management services, for a maximum of two years within the NHS programme. Supply has been constrained at times, and prescribers have been reminded not to use Ozempic for weight loss, to protect supply for people with diabetes. Outside the NHS, semaglutide can only be supplied against a prescription issued after a clinical assessment.
What is not lawful is buying semaglutide without a prescription, or a seller advertising it to the public. Products sold online as "research" semaglutide, or as filled pens from unknown sources, are unlicensed: no regulator has checked what they contain, how much is in them, or whether they are sterile. The MHRA has warned repeatedly about counterfeit and unlicensed weight-loss injections and has taken enforcement action against sellers. The trial figures on this page describe the licensed medicine; they say nothing about an unlicensed copy.
Semaglutide, tirzepatide and retatrutide: reading them side by side
Semaglutide acts on one receptor; tirzepatide adds a second; retatrutide, still in trials, adds a third. In head-to-head and cross-trial comparisons, average weight loss rises across that sequence, and so, broadly, do gastrointestinal side effects. Semaglutide has the longest licensed track record and the largest body of real-world safety data. Tirzepatide is licensed and newer. Retatrutide has no licence and only phase 2 data. Our articles on tirzepatide and retatrutide cover each in the same format as this one, so the figures can be compared like for like.
How to read a semaglutide claim
- Check which product and which dose. A diabetes trial at 1 mg and a weight trial at 2.4 mg answer different questions.
- Check whether the figure includes lifestyle support and how long the trial ran.
- Check whether side effects are reported next to the benefit.
- Check whether the source sells the product. A licensed medicine is prescribed, not marketed to you.
Oral semaglutide: how Rybelsus differs
Semaglutide is also licensed as a daily tablet, Rybelsus, for type 2 diabetes only. Peptides are normally destroyed in the stomach, so the tablet pairs semaglutide with an absorption enhancer and has to be taken in a particular way: once a day on an empty stomach, with no more than half a glass of water, at least 30 minutes before the first food, drink or other medicine of the day. The licensed schedule starts at 3 mg daily for 30 days, then 7 mg, with 14 mg as the maximum if more blood-sugar control is needed. Only a small fraction of an oral dose is absorbed, which is why the tablet strengths are so much larger than the injected ones and why the two cannot be compared milligram for milligram. Rybelsus is not licensed for weight management, and "oral semaglutide" sold online for weight loss is not this product.
Muscle, "Ozempic face" and the things the trials measured less well
Two concerns come up constantly in searches. The first is loss of muscle alongside fat. Body-composition sub-studies in the STEP programme found that lean mass fell as well as fat mass, as it does with any substantial weight loss, while the proportion of lean mass in the body improved. Whether the lean loss matters for strength or health in the long run, and how much resistance training and protein intake offset it, are open questions that later trials are addressing; the honest position is that the drug reduces weight of all kinds and that preserving muscle is a matter of what accompanies it. The second is the change in facial appearance that comes with rapid fat loss, sometimes called "Ozempic face". It is not a drug effect in the pharmacological sense; it is what losing a lot of fat quickly does to a face, and it happens with any method that produces the same loss.
Questions the licence does not answer
A licence is precise about what was studied and silent about what was not. Semaglutide's trials excluded pregnancy and the licence advises stopping at least two months before trying to conceive. Long-term use beyond a few years is still being characterised through real-world data. Its effects in people with a normal body-mass index who take it to lose a small amount of weight were never studied, and its licence does not cover that use. People with a history of eating disorders were largely excluded from the trials. None of these gaps is a secret; they are written into the product information, and they are the questions a prescriber weighs and an online seller does not ask.
This article is educational content only and is not medical advice, diagnosis or a recommendation to use any medicine. Semaglutide is a prescription-only medicine; the doses described are those set by its UK licences and used in clinical trials, and they are not instructions for use. Anyone considering treatment for weight or blood sugar should speak to a GP, pharmacist or other qualified prescriber. Vivera Education sells nothing.
Frequently asked
- What is the semaglutide dose for weight loss?
- The UK licence for Wegovy starts at 0.25 mg once a week and increases every four weeks through 0.5 mg, 1 mg and 1.7 mg to a maintenance dose of 2.4 mg weekly. The lower doses are for building tolerance; 2.4 mg is the dose the weight trials studied. A prescriber sets and adjusts the schedule.
- What is the semaglutide dose for type 2 diabetes?
- Ozempic starts at 0.25 mg once weekly for four weeks, then 0.5 mg weekly, with increases to 1 mg and, if needed, 2 mg weekly at intervals of at least four weeks, according to blood-sugar response. Ozempic and Wegovy are the same molecule at different licensed doses for different purposes.
- How is semaglutide taken?
- As a once-weekly injection under the skin of the abdomen, thigh or upper arm, using the licensed pre-filled pen, on the same day each week, with or without food. A pharmacist or clinician demonstrates the pen and the patient is reviewed as the dose increases. An oral tablet form (Rybelsus) is licensed for type 2 diabetes with its own daily schedule.
- How much weight do people lose on semaglutide?
- In the 68-week STEP 1 trial of 1,961 adults without diabetes, average weight change was about 14.9% on 2.4 mg semaglutide against about 2.4% on placebo, both alongside lifestyle support. Around a third of those on semaglutide lost 20% or more. Results varied widely between individuals.
- What are the side effects of semaglutide?
- Most commonly nausea, diarrhoea, vomiting, constipation and abdominal pain, mostly mild to moderate and most frequent during dose increases. Less common but serious risks on the licence include gallbladder disease, pancreatitis and, with insulin or sulfonylureas, low blood sugar. The patient leaflet lists the full profile.
- Is semaglutide available on the NHS for weight loss?
- Yes, within limits. NICE recommended Wegovy in March 2023 for adults meeting body-mass index and weight-related condition criteria, prescribed through specialist weight-management services for up to two years. Ozempic is prescribed for type 2 diabetes. Outside the NHS it can only be supplied against a prescription issued after a clinical assessment.
- Can I buy semaglutide without a prescription in the UK?
- No. Semaglutide is a prescription-only medicine and cannot lawfully be sold to the public without a prescription or advertised to the public. Products sold online as "research" semaglutide are unlicensed, and no regulator has checked what they contain or whether the dose on the label is real.
- What happens when semaglutide is stopped?
- In the STEP trials that followed people after stopping, a large part of the lost weight returned over the following year. The licence treats it as an ongoing treatment alongside diet and activity, not a course, and stopping is a decision for the patient and prescriber together.
The studies and sources behind this page
Lessons on this topic
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Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.