Where the curves come from

Each medication is modelled from checkpoints taken from its pivotal trial data — percentage weight loss at specific week markers — with linear interpolation between them. The projection runs to week 68, the endpoint used by most of the major obesity trials, and does not extrapolate beyond it.

Projected weight at any week is simply starting weight multiplied by one minus the interpolated percentage loss. The placebo curve is included deliberately, because roughly 3% loss occurs in trial placebo arms and it is the correct baseline for judging what the drug itself contributes.

Why the average is not your outcome

Mean weight loss conceals enormous individual variation. In the major trials some participants lose more than 30% and others lose almost nothing on the same drug at the same dose. A projection line is the centre of a wide distribution, not a prediction for one person.

Trial participants also receive structured dietary counselling, titration supervision and regular contact that ordinary prescribing does not include. Real-world results typically fall below trial averages for that reason alone, independent of the drug.

Plateaus are expected

Every curve here flattens. Weight loss on GLP-1 agonists is fastest in the early months and slows markedly toward the trial endpoint as energy expenditure adapts and appetite signalling re-equilibrates. A plateau at month eight is the expected shape of the curve, not evidence of failure or tolerance.

The steepest section is also the point at which lean mass loss is most likely, which is why resistance training and adequate protein intake matter most early rather than late.

Frequently asked questions

How much weight will I lose on semaglutide or tirzepatide?

Trial averages are the only honest starting point, and individual results vary enormously around them — some participants lose over 30% while others lose very little at the same dose. This tool projects the trial average trajectory for your starting weight, but treat it as the centre of a wide distribution rather than a forecast.

Why has my weight loss plateaued?

Because that is the shape of the curve. Weight loss is fastest in the first months and slows toward the one-year mark as energy expenditure adapts and appetite regulation re-equilibrates at the new weight. Every trial curve flattens. A plateau is expected, not a sign the medication has stopped working.

Why is a placebo curve included?

Because roughly 3% weight loss occurs in trial placebo arms, driven by the dietary support and monitoring everyone in a trial receives. The drug's real contribution is the gap between its curve and placebo, not the full height of its own curve.

Will real-world results match the trial projections?

Usually not quite. Trial participants get dietary counselling, supervised titration and regular follow-up that most people prescribed these drugs do not receive, and adherence in trials is higher than in practice. Real-world outcomes generally fall somewhat below trial averages for those reasons alone.