What the OASIS 4 semaglutide trial actually found

How OASIS 4 was designed and why 13.6% is the right headline number

Pharmaceutical trials measure outcomes in different ways, and OASIS 4 is no exception to the complexity. The trial randomised 307 adults (people with a BMI of 30 or above, or 27 or above with at least one weight-related condition, and no type 2 diabetes) to either once-daily oral semaglutide (titrated from 1.5mg up to a 25mg maintenance dose) or a matching placebo, alongside standard lifestyle guidance. Both groups followed the same dietary and activity advice, so the difference in outcomes reflects the medicine's contribution.

The primary result (13.6% average body-weight reduction at week 64) is measured on an intention-to-treat basis. That means it includes everyone who was randomised, whether they completed every dose or not. It is the honest, conservative figure: the one that reflects how medicines behave in the real world rather than in an idealised adherent population. When researchers looked only at participants who took the tablets as prescribed throughout, the average climbed to around 16.6%. Both numbers are real; which one you cite depends on what you are trying to communicate. Novo Nordisk's announcement of the MHRA approval in June 2026 quoted both, which is why you may see 'about 17%' referenced in some places, that figure applies to fully adherent participants only.

A common assumption is that oral semaglutide must be substantially less effective than the injection because it is a tablet. OASIS 4 does not entirely support that view. The 13.6% average sits meaningfully above placebo and within a range that many patients find clinically significant. The injection's STEP 1 trial, run at the 2.4mg weekly maintenance dose, reported roughly 15% average loss at 68 weeks, a higher figure, but from a different trial design, different follow-up duration and different patient population. Direct comparisons between those two numbers should be made carefully, and our pages covering semaglutide 1 and semaglutide 2 go into more detail on how the dosing stages differ and what patients typically experience at each step.

What OASIS 4 found about side effects and tolerability

Gastrointestinal effects were the dominant finding on tolerability. Around 74% of participants in the semaglutide group reported at least one GI side effect during the trial, compared with 42% in the placebo group. Nausea, diarrhoea, vomiting and constipation were the most frequently mentioned. The good news from the data is that the majority of these events were rated mild to moderate in severity and tended to appear early (particularly around dose increases) then settle as the body adjusted.

This pattern is consistent with what the NHS semaglutide medicines page describes for semaglutide broadly: GI effects are most noticeable when the dose goes up and often improve within a couple of weeks. The titration schedule for Wegovy tablets (starting at 1.5mg and stepping up through 4mg and 9mg before reaching 25mg, with at least a month at each level) is designed specifically to manage this. Slower titration gives the gut time to adapt.

Serious adverse events occurred in both groups, as would be expected in any 64-week trial in an older, heavier population with comorbidities; no new safety signals emerged that were not already known from the injectable semaglutide programme. If you experience severe or persistent stomach pain that radiates to your back, that warrants prompt medical attention regardless of what medicine you are taking.

Who the OASIS 4 population resembled, and what that means for eligibility

Understanding who was in the trial helps you gauge how applicable the results are. OASIS 4 participants were adults with a BMI of at least 30, or at least 27 with a weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. People with type 2 diabetes were excluded, separate trials address that population. The licensed eligibility criteria for Wegovy tablets in the UK mirror this: BMI 30 or above, or 27 to 29.9 with at least one qualifying condition.

It is worth being clear about what a clinical trial result is not: it is not a personal prediction. Thirteen percent is a population average. Some participants lost more; some lost less. Factors including starting weight, how consistently the medicine is taken, dietary habits, physical activity and individual biology all shape the outcome. Our clinical team can give you a more grounded picture of what to expect based on your specific health background, which is part of what a proper clinical assessment is for.

For more background on semaglutide as a medicine and how the oral and injectable versions compare, the semaglutide overview on this site covers the licensing history, mechanism and UK approval timeline. If you want to understand the wider OASIS trial programme (OASIS 4 was one of several phase 3 studies) that page sets out how the different arms relate to each other.

From trial evidence to a treatment decision

OASIS 4 gave the MHRA what it needed to approve the first oral GLP-1 for weight management in the UK on 11 June 2026. That is a significant regulatory milestone, but trial approval and personal suitability are different questions. Wegovy tablets are a prescription-only medicine; a prescriber reviews your health history, current medications and BMI before any treatment begins. There is no shortcut around that step, and no reputable service would suggest otherwise.

What the OASIS 4 data does tell you is that the medicine has a meaningful, replicated evidence base behind it. If you are considering whether oral semaglutide might be appropriate for you, our frequently asked questions cover the practical points patients most often raise, and you can find out how treatment pricing fits into the wider picture on the Wegovy pricing page. When you are ready to take the next step, our weight-loss treatments overview explains what the consultation process looks like from start to finish.