ATTAIN-1: the orforglipron pill for weight loss over 72 weeks

Why this study matters

Orforglipron is an experimental medicine. It is not approved in Canada as of September 2026, and this study is research only. It is a small-molecule GLP-1 receptor agonist taken as a once-daily pill rather than an injection. ATTAIN-1 is the large, late-stage trial that followed the earlier phase 2 dose-finding study. Phase 3 trials are the ones regulators usually rely on, so this is the study Canadian readers are most likely to hear about if the medicine is ever reviewed for approval here.

Who was in the study

The trial enrolled 3127 adults. All had obesity and none had diabetes. It ran for 72 weeks and was multinational, meaning it was run in more than one country. The published summary we reviewed does not report the age range, the countries, or the average starting weight.

What the researchers did

This was a phase 3, randomized, double-blind trial. Randomized means people were assigned to a group by chance. Double-blind means neither participants nor study staff knew who was taking the medicine and who was taking placebo, an inactive pill that looks identical.

Participants took orforglipron at 6 mg, 12 mg or 36 mg, or placebo, once a day for 72 weeks, assigned in a 3:3:3:4 ratio. All groups received the pill as an add-on to a healthy diet and physical activity. The primary end point, meaning the main result the trial was designed to measure, was the percentage change in body weight from the start to week 72.

The result was analysed with the treatment-regimen estimand in the intention-to-treat population. An estimand is the precise question the statistics answer. This one counts everyone who was randomized, whether or not they kept taking their pills, which gives a picture of what happens when the medicine is prescribed in real life rather than only among people who stick with it.

What they found

At week 72, the average change in body weight was -7.5% (95% confidence interval -8.2 to -6.8) with 6 mg, -8.4% (95% CI -9.1 to -7.7) with 12 mg and -11.2% (95% CI -12.0 to -10.4) with 36 mg, compared with -2.1% (95% CI -2.8 to -1.4) with placebo. A confidence interval is the range of values the data are reasonably consistent with. Each dose differed from placebo with P below 0.001 (R32-C61).

Among people in the 36 mg group, 54.6% lost at least 10% of their body weight, 36.0% lost at least 15% and 18.4% lost at least 20%. In the placebo group the figures were 12.9%, 5.9% and 2.8%.

Waist circumference, systolic blood pressure, triglycerides and non-HDL cholesterol improved significantly with orforglipron compared with placebo. The published summary we reviewed does not give those numbers, and it does not report a between-group difference in weight with its own confidence interval.

Side effects and people who stopped

Adverse events led to stopping treatment in 5.3 to 10.3% of people across the orforglipron groups and in 2.7% of the placebo group (R32-C62). The published summary we reviewed does not give the exact rate for each dose, or the overall number of people who left the trial. The most common side effects with orforglipron were gastrointestinal, meaning stomach and bowel symptoms, and these were mostly mild to moderate. The authors describe the side-effect profile as consistent with other GLP-1 receptor agonists.

What this study does not tell you

• Orforglipron is not approved in Canada as of September 2026. This is evidence about an investigational medicine.
• The trial excluded people with diabetes, so the results do not apply to them.
• Our summary is based on the abstract only. Details such as the age range, countries, starting weight and results by dose for stopping are not available to us.
• The trial ran for 72 weeks. It does not show what happens over longer periods or after the pill is stopped.
• The intention-to-treat analysis includes people who stopped taking the pill, so the average effect among people who kept taking it may differ.
• Do not compare these percentages with numbers from trials of injectable medicines. Different trials enrol different people and use different methods.
• The trial was funded by the company that makes the medicine.

What it means in Canada

Orforglipron is not approved in Canada as of September 2026. ATTAIN-1 is the kind of trial a regulator would review, but that review has not led to a Canadian approval as of our review date. You can follow emerging medicines on our medicines page. For medicines available in Canada, see semaglutide in Canada and tirzepatide in Canada, and public drug coverage by province.

Related reading

Other studies in this library that bear on the same question.

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