Orforglipron Trial Results: What ATTAIN and ACHIEVE Found

The headline orforglipron trial results come from ATTAIN-1, a 72-week phase 3 trial in 3,127 adults with obesity or overweight and no diabetes. At the top dose, average weight loss was 12.4% of body weight versus 0.9% on placebo, according to the UK product information; the published paper's primary analysis, which also counts results after people stopped treatment, gives 11.2% versus 2.1%. Trials in type 2 diabetes showed lower blood sugar and weight, including bigger reductions than oral semaglutide in a head-to-head study.

Figures below come from the published papers and the UK Summary of Product Characteristics (SmPC), checked as of September 2026. This is information only, not medical advice: Foundayo (orforglipron) is a prescription-only medicine, and a qualified prescriber decides whether it is suitable.

Orforglipron trial results: which studies have reported?

Eli Lilly ran two phase 3 programmes, ATTAIN for weight management and ACHIEVE for type 2 diabetes, after phase 2 studies.

• Phase 2 (New England Journal of Medicine, 2023): 272 adults without diabetes lost 9.4% to 14.7% over 36 weeks, versus 2.3% on placebo.
• ATTAIN-1 (NEJM, September 2025): 3,127 adults without diabetes, 72 weeks.
• ATTAIN-2 (The Lancet, November 2025): 1,613 adults with type 2 diabetes, 72 weeks.
• ATTAIN-MAINTAIN (Nature Medicine, May 2026): 376 people moving on from injectable treatment, 52 weeks.
• ACHIEVE-1, -2, -3 and -5: diabetes trials lasting 40 to 52 weeks.

Why the trial doses do not match UK tablets

The ATTAIN trials used 6 mg, 12 mg and 36 mg capsules; some ACHIEVE trials also used 3 mg. The SmPC says similar efficacy and safety can be expected from the 5.5 mg, 9 mg and 17.2 mg tablets, but the two forms are not interchangeable milligram for milligram. The 14.5 mg tablet was not a dose group in ATTAIN-1 or ATTAIN-2. Our dosage page explains the step-up schedule.

What were the ATTAIN-1 weight-loss results?

ATTAIN-1 enrolled adults with a BMI of 30 or more, or 27 or more with a weight-related condition such as high blood pressure, and no type 2 diabetes. Average age was 45 and average BMI 37.0. The SmPC reports these average weight changes at 72 weeks:

• 5.5 mg tablet (6 mg capsule): 7.8% lost
• 9 mg tablet (12 mg capsule): 9.3% lost
• 17.2 mg tablet (36 mg capsule): 12.4% lost
• Placebo: 0.9% lost

At the top dose, 59.6% lost at least 10% of their body weight and 39.6% lost at least 15%, compared with 8.6% and 3.6% on placebo. Among 1,128 participants with prediabetes, 87.7% to 91.3% on orforglipron had normal blood sugar at week 72, versus 42.4% on placebo. A body-scan sub-study found the loss was mainly fat, though lean mass also fell.

Why you may also see 11.2%

Lilly calls 12.4% the "efficacy estimand": the expected result had everyone stayed on treatment. The NEJM paper's primary "treatment-regimen estimand" counts results whether or not people kept taking the medicine: 11.2% versus 2.1% on placebo. Both are genuine; check which a source quotes.

What did ATTAIN-2 find in type 2 diabetes?

ATTAIN-2 tested the same doses for 72 weeks in 1,613 adults with type 2 diabetes and a BMI of 27 or more. The SmPC reports average weight loss of 5.5%, 7.8% and 10.5%, versus 2.2% on placebo; the Lancet paper's primary analysis gives 9.6% versus 2.5% at the top dose. HbA1c, a measure of longer-term blood sugar, fell by 1.8 percentage points at the top dose from about 8%, versus 0.1 on placebo.

How did orforglipron do in the diabetes trials?

• ACHIEVE-1 (559 people, 40 weeks): from an average HbA1c of about 8.0%, HbA1c and body weight fell more on orforglipron than on placebo.
• ACHIEVE-2 (962 people on metformin, 40 weeks): HbA1c fell more on orforglipron than with dapagliflozin.
• ACHIEVE-3 (1,698 people on metformin, 52 weeks): an open-label head-to-head against oral semaglutide. Both orforglipron doses lowered HbA1c more than both semaglutide doses, and the SmPC reports weight loss of 9.2% on orforglipron 36 mg versus 5.3% on semaglutide 14 mg. Gastrointestinal side effects and stopping because of side effects were more common with orforglipron.
• ACHIEVE-5 (546 people on insulin glargine, 40 weeks): HbA1c fell more on orforglipron than on placebo, without more clinically significant low blood sugar.

ACHIEVE-3 used diabetes doses of oral semaglutide, not weight-loss doses.

Does weight stay off after switching from injections?

ATTAIN-MAINTAIN moved people who had lost weight on tirzepatide or semaglutide to orforglipron or placebo for 52 weeks. Among those whose weight had plateaued, the tirzepatide group kept an estimated 74.7% of their loss on orforglipron versus 49.2% on placebo; the semaglutide group kept 79.3% versus 37.6%. It had no comparison group staying on injections and lasted one year.

What side effects did the trials report?

In the weight-management trials, gastrointestinal effects such as nausea, diarrhoea, constipation and vomiting affected 60.1% to 68.7% of people on orforglipron versus 36.3% on placebo. Most were mild or moderate, and 3.7% to 6.8% stopped treatment because of them, versus 0.6% on placebo. In ATTAIN-1, 5.3% to 10.3% stopped because of any adverse event, versus 2.7%. The SmPC also lists gallstones as common and acute pancreatitis as uncommon.

Average pulse also rose, by 6.7 to 8.6 beats per minute at its peak during dose increases and 3.9 to 5.2 at week 72. Across the placebo-controlled phase 3 trials, major cardiovascular events occurred in 0.94% of people on orforglipron and 1.04% on placebo; the SmPC says this does not suggest increased cardiovascular risk, which is not the same as proven heart benefit. See our side effects page, and report suspected side effects through the MHRA Yellow Card scheme.

What do the results not tell us?

• No head-to-head against weight-loss injections. Semaglutide 2.4 mg gave around 15% in STEP 1 and tirzepatide 15 mg around 21% in SURMOUNT-1, in separate trials. See our Foundayo vs Mounjaro comparison.
• Limited long-term data: the main weight-loss trials lasted 72 weeks.
• Sponsor funding: Eli Lilly funded all the trials described here.
• Trial conditions: regular visits and lifestyle counselling may not match everyday care.

Where do the results leave Foundayo in the UK?

The US Food and Drug Administration approved Foundayo for weight management on 1 April 2026. The MHRA authorised it on 10 August 2026 for weight management and type 2 diabetes, making the UK the first European country to approve it. As of September 2026 it is not available on the NHS; NICE's appraisal (ID6516) is provisionally expected to publish on 27 January 2027. See our UK availability page and development page.

Frequently asked questions

Related reading

• Foundayo side effects: what the UK leaflet and trials report
• How orforglipron works: the science behind Foundayo
• Foundayo vs Mounjaro: tablet and injection compared