What it means
Trials report results in more than one way. The efficacy estimand, sometimes called the trial product estimand, looks at what happens while people are actually on the drug. It sets aside data after someone stops treatment or starts other weight-loss treatments.
That makes it a good answer to "what can this drug do when taken as directed?" It is usually a bit higher than the treatment-regimen result because people who stopped early are not pulling the average down.
Both numbers are valid. They answer different questions, so always check which one a headline quotes.
When you compare two drugs from different trials, make sure you are comparing the same estimand from each. Mixing them can make one drug look better than it is.
Why it matters
Sunny Weigh labels which estimand each projection uses so you can compare drugs fairly.