The clearest data on this is the extension of the STEP-1 trial. Participants lost about 17% of body weight over 68 weeks on semaglutide. After they stopped the peptide, they were followed for another year.

By the end of that year, they had regained about 12 of those 17 percentage points, leaving them about 6% below where they started. That's two-thirds of the original loss recovered.

For tirzepatide, the SURMOUNT-4 trial set up the same kind of comparison. People who switched to placebo regained about 14% of body weight over the following year. People who stayed on the peptide lost an additional 5.5%.

The body's setpoint, appetite signaling, and the lifestyle structure that the peptide had been smoothing all came back when the peptide was removed.