Foundayo vs. Wegovy: What 72 Weeks of Trial Data Really Show

"Lose up to 16.6%." "Lose an average of 27 pounds." Weight loss medicines arrive with bold headline numbers, and the two daily GLP-1 tablets now prescribed in the UK are no exception.

But trial results are more than a single figure. How long the study ran, who took part, how many people stopped early and which way the data were counted can all move the number by several percentage points.

So here is what the main trials behind Foundayo and the Wegovy pill actually found, what they can and can't tell you, and how to use that information when choosing a treatment.

Meet the two trials

ATTAIN 1 (Foundayo). Eli Lilly's main obesity trial enrolled 3,127 adults with obesity, or overweight plus a weight related health condition, and no diabetes. Participants were spread across ten countries and randomly assigned to one of three orforglipron doses or a placebo, alongside diet and exercise advice, for 72 weeks. The full results were published in the New England Journal of Medicine in September 2025. The trial's top dose was 36 mg, which corresponds to the 17.2 mg tablet now prescribed as Foundayo.

OASIS 4 (Wegovy pill). Novo Nordisk's trial was much smaller, with 307 adults without diabetes. Two thirds took oral semaglutide 25 mg and one third took placebo, plus lifestyle support. Here is a detail many articles skip: OASIS 4 ran for 64 weeks of treatment, not 72. It was also published in the New England Journal of Medicine in 2025.

So while Foundayo has a true 72 week dataset, the Wegovy pill's figures come from a slightly shorter study.

The results side by side

At the highest dose, the Wegovy pill produced more weight loss on average. Both beat placebo by a wide margin.

	Foundayo (ATTAIN 1, top dose)	Wegovy pill (OASIS 4, 25 mg)
Participants	3,127	307
Treatment length	72 weeks	64 weeks
Average weight loss, everyone counted	11.2%	13.6%
Placebo, everyone counted	2.1%	2.2%
Average weight loss, if stayed on treatment	12.4%	16.6%
Stopped due to side effects	10.3%	6.9%

On the top Foundayo dose, 55% of people lost at least 10% of their body weight and 19% lost at least 20%. With the Wegovy pill, about one in three people who stayed on treatment lost 20% or more.

The lower Foundayo doses also worked, producing average losses of 7.5% and 8.4%. For a closer look at the dose by dose picture, read our breakdown of Foundayo weight loss results.

Why this isn't a true head to head

It is tempting to read the table as a straight contest. It isn't, for four reasons.

Different people. OASIS 4 was 79% women and 92% White. ATTAIN 1 was far larger and more varied, including large groups from Asia and South America. Average starting weight and background differ, and both affect how much weight people lose.

Different lengths. Sixty four weeks versus 72 weeks may sound close, but weight curves keep shifting late in treatment.

Different sizes. A trial of 307 people produces a less precise estimate than one of over 3,000. The Wegovy pill's true average could sit a little higher or lower than 13.6%.

No direct comparison. Neither trial tested the two pills against each other. Comparing results across separate trials gives a useful rough guide, not a verdict.

The fair conclusion? The Wegovy pill looks somewhat stronger on average, but the true gap is probably smaller than the headline numbers suggest.

Two numbers for every result: which one matters to you?

You may have noticed each pill has two weight loss figures. That isn't spin. Trials count results in two ways.

The first counts everyone who started, including people who missed doses, stopped early or switched treatment. For Foundayo that gives 11.2%. For the Wegovy pill, 13.6%. This is closer to what happens in real life.

The second estimates what happens if everyone keeps taking the medicine as prescribed. That gives 12.4% for Foundayo and 16.6% for the Wegovy pill. This is closer to what you can expect if you stay on track.

And staying on track isn't guaranteed. In ATTAIN 1, about 75% of participants were still taking their treatment at the end. Around 24% of people on the top Foundayo dose stopped early for any reason. In OASIS 4, 167 of the 205 people on semaglutide completed the trial.

The practical message is simple: the medicine only works on the days you take it, and take it correctly.

What the trials showed about side effects

Both tablets behaved much like the injections. Stomach and gut symptoms were the most common, usually mild to moderate and worst during dose increases.

In ATTAIN 1, about a third of people on Foundayo reported nausea. In OASIS 4, 46.6% of people on the Wegovy pill reported nausea and 30.9% reported vomiting, compared with 18.6% and 5.9% on placebo.

Serious side effects were uncommon with both. Slightly more people stopped Foundayo at the top dose because of side effects (10.3%) than stopped the Wegovy pill (6.9%), though again these come from different trials.

What the data mean for you

Trial averages describe groups, not individuals. Some people on either pill lose far more than the average, and some lose less.

The Wegovy pill may be the better fit if you want the highest average result a tablet currently offers and you are happy to take it on an empty stomach, then wait 30 minutes before eating or drinking.

Foundayo may be the better fit if you value flexibility. It has no food or water rules, so you can take it whenever suits you. A slightly lower average you reliably achieve can beat a higher one you struggle to keep up.

Our Daily Weight Loss Tablets service can help you weigh these trade offs with a clinician who knows your health history.

If maximum weight loss is the priority, injections still lead the field. Weekly tirzepatide, for example, produced average losses above 20% in its main trials. Mounjaro and Wegovy injections are worth considering if a weekly routine suits you better than a daily one.

Frequently asked questions

Which pill caused more weight loss in trials?

The Wegovy pill, on average. It produced 13.6% weight loss over 64 weeks versus 11.2% for top dose Foundayo over 72 weeks, counting everyone who started. The trials were separate, so the comparison is approximate.

Was the Wegovy pill tested for 72 weeks?

No. Its main trial, OASIS 4, involved 64 weeks of treatment. Foundayo's ATTAIN 1 trial ran for 72 weeks.

Why do I see different percentages for the same pill?

Trials report one figure counting everyone who started and another estimating results if everyone stayed on treatment. The second is always higher.

How many people lost 20% or more?

About 19% of people on top dose Foundayo, and roughly one in three people who stayed on the Wegovy pill.

Were the side effects different?

They were similar in type, mostly nausea, vomiting, diarrhoea and constipation. A few more people stopped Foundayo at the top dose because of side effects.

Do lower doses of Foundayo still work?

Yes. The lower doses in ATTAIN 1 produced average weight loss of 7.5% and 8.4%, compared with 2.1% on placebo.

Will I get the same result as the trial?

Nobody can promise that. Trial participants had regular support and monitoring, which helps. Your result depends on your dose, your consistency and the lifestyle changes you make alongside treatment.

The bottom line

The trial data point the same way: the Wegovy pill delivers somewhat more weight loss on average, while Foundayo offers solid results with far fewer rules about how you take it. Neither number tells you which pill will work best for you. Your health, your habits and your goals do.

Want help reading the evidence against your own situation? The clinical team at Weight Medics can talk you through both tablets and build a plan that suits your life.