Important: This page reflects the UK regulatory position on 14 August 2026. Foundayo was authorised by the MHRA on 10 August 2026. NICE is still appraising orforglipron for weight management, and the MHRA states that it is not currently available through the NHS. [1][6]
What did the main Foundayo weight-loss trial find?
The strongest evidence for Foundayo weight loss effectiveness comes from ATTAIN-1, a Phase 3 randomised, double-blind, placebo-controlled trial involving 3,127 adults. Participants had obesity, or overweight with at least one weight-related health condition, and did not have diabetes. They received orforglipron or placebo once daily for 72 weeks alongside diet and physical-activity support. [2]
The trial population is important when interpreting the headline number. Participants were around 45 years old on average, with a mean starting body weight of 103.2 kg and a mean BMI of 37.0. Around 64% were women, and 36% had prediabetes. [2]The table below shows the average change in body weight at 72 weeks using both statistical approaches reported in ATTAIN-1.
|
ATTAIN-1 trial dose
|
Treatment-regimen estimand
|
Efficacy estimand
|
|
6 mg
|
-7.5%
|
-7.8%
|
|
12 mg
|
-8.4%
|
-9.3%
|
|
36 mg
|
-11.2%
|
-12.4%
|
|
Placebo
|
-2.1%
|
-0.9%
|
All three orforglipron doses produced significantly greater average weight reduction than placebo. [2]
The 6 mg, 12 mg, and 36 mg figures refer to the investigational capsule formulation used in the Phase 3 trial. Pharmacokinetic testing later showed these doses to be bioequivalent to 5.5 mg, 9 mg, and 17.2 mg tablets respectively. The MHRA's UK authorisation lists tablet strengths up to 17.2 mg. [1][5]
Why some sources say 11.2% and others say 12.4%
Both numbers come from ATTAIN-1. They are not competing versions of the same result; they answer slightly different questions.
The treatment-regimen estimand includes participants according to the treatment they were assigned, regardless of whether they later stopped taking the study medicine or used prohibited weight-management treatment. On the highest studied dose, average weight change was -11.2%. [2]
The efficacy estimand estimates what the result would have looked like if participants had remained on the assigned treatment and had not used prohibited weight-management treatment. On the highest dose, average weight change was -12.4%. [2]
For a consumer article, 11.2% is the more useful headline starting point because it preserves more of the variation created by people stopping treatment or needing other treatment. It should not, however, be described as a real-world result. ATTAIN-1 was still a controlled clinical trial.
This distinction matters because a statement such as 'Foundayo causes 12.4% weight loss' removes the conditions attached to that number. A more accurate summary is that the highest studied dose produced an average 11.2% reduction under the treatment-regimen analysis and 12.4% under the efficacy analysis over 72 weeks. [2]
The numbers of people who lost 5%, 10%, 15% or 20% of their weight
A trial average does not show how widely individual results were spread. The response thresholds from ATTAIN-1 give a more useful picture of variation.
|
Weight reduction reached at 72 weeks
|
Highest-dose orforglipron
|
Placebo
|
|
At least 5%
|
71.8%
|
26.8%
|
|
At least 10%
|
54.6%
|
12.9%
|
|
At least 15%
|
36.0%
|
5.9%
|
|
At least 20%
|
18.4%
|
2.8%
|
Figures use the treatment-regimen analysis. [2]
The practical point is not that 11.2% is the result someone should expect. It is that people responded differently. Just over half of participants on the highest dose reached at least 10% weight reduction, while a little over one-third reached at least 15%. Around 18% reached at least 20%. [2]
Likewise, the 71.8% figure for at least 5% weight loss means 28.2% did not reach the 5% threshold. It does not mean that 28.2% lost no weight at all.
This is why converting the average into a personal forecast — for example, saying that someone who weighs 100 kg should expect to lose 11.2 kg — would overstate what the trial can tell an individual.
Does Foundayo work better at higher doses?
ATTAIN-1 showed a dose-response relationship: higher studied doses produced larger average weight reductions. [2]
That does not mean the highest dose is automatically the best dose for every person. Effectiveness has to be considered alongside tolerability. In ATTAIN-1, discontinuation because of adverse events increased from 5.3% on the lowest studied dose to 10.3% on the highest, compared with 2.7% on placebo. Gastrointestinal effects were the most common adverse events. [2]
The dose-response results are not a reason to increase Foundayo yourself or aim for the maximum dose. UK treatment uses staged dose escalation, and dose changes should follow the prescribing instructions and clinical assessment.
What were the results for people with type 2 diabetes?
ATTAIN-2 studied a different population: 1,613 adults with obesity or overweight and type 2 diabetes. Participants received orforglipron or placebo for 72 weeks. [3]
On the highest studied dose, average body-weight reduction was 9.6% under the treatment-regimen analysis, compared with 2.5% with placebo. Under the efficacy analysis, the corresponding highest-dose result was about 10.5%. [3]
Those figures should not be blended with ATTAIN-1 into one universal 'Foundayo effectiveness' number. People with type 2 diabetes were studied separately, and the average weight reduction was lower than in the ATTAIN-1 population without diabetes. [2][3]
Can Foundayo help maintain weight loss after Mounjaro or Wegovy?
There is direct evidence for a specific maintenance scenario from ATTAIN-MAINTAIN, a Phase 3b randomised trial. Participants had previously completed 72 weeks of treatment with tirzepatide or semaglutide in the SURMOUNT-5 study and were then assigned to orforglipron or placebo for another 52 weeks. [4]
Among participants who had reached a body-weight plateau after tirzepatide, the model-based estimate was that 74.7% of the previous weight reduction was maintained with orforglipron, compared with 49.2% with placebo. Among those who had plateaued after semaglutide, the corresponding figures were 79.3% with orforglipron and 37.6% with placebo. [4]
These results support the conclusion that orforglipron reduced weight regain compared with placebo after stopping the injectable treatment in this study population. They do not show that everyone switching to Foundayo will maintain 75–80% of their previous weight loss.
The trial also does not establish that switching is equivalent to staying on tirzepatide or semaglutide, or that the same maintenance percentages apply to people who initially lost weight with Foundayo itself. [4]
What else changed besides body weight?
ATTAIN-1 also reported improvements in waist circumference, systolic blood pressure, triglycerides, and non-HDL cholesterol compared with placebo. [2]
Those findings are relevant because obesity treatment is not only about the number on the scales. However, these are cardiometabolic risk markers rather than direct cardiovascular-outcome results.
How does Foundayo effectiveness compare with Wegovy or Mounjaro?
There is no randomised weight-management trial directly comparing Foundayo with Wegovy or Mounjaro in the same obesity-treatment population. That means percentages taken from separate trials should not be treated as a league table proving which medicine would produce more weight loss for the same person.
There is an important qualification to this. ACHIEVE-3 directly compared orforglipron with oral semaglutide in adults with type 2 diabetes. That trial compared diabetes treatment regimens and was not a Foundayo-versus-Wegovy weight-management trial. It therefore does not answer the question of which medicine is more effective for obesity treatment. [7]
ATTAIN-MAINTAIN also involved people who had previously taken tirzepatide or semaglutide, but it compared orforglipron with placebo after the injectable treatment was stopped. It did not randomise people to continue Mounjaro or Wegovy versus switching to Foundayo. [4]
For someone choosing between treatments, effectiveness is only one part of the clinical decision. Suitability, side effects, other health conditions, dosing preferences, and previous treatment response also matter. Trial averages cannot determine which option is appropriate for an individual.
What do the Foundayo studies not tell us yet?
The current evidence is substantial enough to show that orforglipron produces greater average weight reduction than placebo, but several important questions remain open.
The evidence does not yet tell us with confidence:
- Exactly how much weight a particular person will lose
- How Foundayo performs over several years of continuous treatment in the wider population
- What UK real-world adherence and effectiveness will look like outside controlled trial
- Whether the weight-maintenance results seen after prior tirzepatide or semaglutide apply to other treatment-transition situations
- How Foundayo compares directly with Wegovy or Mounjaro in a head-to-head obesity trial.
The main published ATTAIN-1 results cover 72 weeks. Participants with prediabetes are continuing in an extension phase lasting about 193 weeks in total, so longer-term evidence is still being generated. [8]
That uncertainty should not be filled with personal predictions. A clinical assessment can determine whether a treatment may be suitable, but it cannot turn a trial average into a precise individual outcome.
