Peptide basics

You could not enter the main GLP-1 weight trials below a BMI of 27

This page sets out the body mass index thresholds that governed entry to the major GLP-1 trials, so you can tell whether a published result describes people like the person you are reading about. It contains no dose, schedule or route and is not medical advice.

What the registry records say

Eligibility criteria are filed with the registration, before results exist, and they are public. STEP 1's entry requirement was a body mass index of 30 or above, or 27 or above in the presence of a weight-related condition.¹

SURMOUNT-1 used the same two-tier structure: 30 or above, or 27 or above with at least one listed comorbidity. The SCALE obesity trial of liraglutide set its floor at 30.²⁴

SELECT is the outlier and the most instructive. It required a BMI of 27 or above and established cardiovascular disease, and set a minimum age of 45. It was not a weight trial; it was a trial in people who had already had a cardiovascular event.³

What a threshold does to a result

A headline weight-loss percentage from one of these trials is an average within the enrolled range. It is not an estimate for someone below the floor, because nobody below the floor was in the study.¹

This is the ordinary meaning of an inclusion criterion and it is not a criticism of the trials. Setting a floor is how you study a condition rather than a general population. It just means the result travels with the floor attached.¹²

The adolescent trial counts differently

The semaglutide trial in 12 to 17 year olds did not use an absolute BMI. It used the 95th percentile for age and sex, or the 85th percentile with a weight-related condition, following growth charts rather than a single number.⁵

That is standard practice in paediatrics, because a fixed BMI means different things at different ages. It also means adult and adolescent results are not directly comparable on this axis.⁵

How to use this when reading a claim

When a figure is quoted, the question is which trial and who could enter it. Both are one click away on the registry record, and the eligibility section is usually the fastest way to tell whether a result describes the person it is being sold to.¹

Common questions