Modelling to extrapolate weight loss in clinical trials for pharmacotherapies into long-term outcomes is uncertain and associated with a high decision risk because of the substantial size of the eligible populations and duration of treatment.

Predicting long-term body mass index trajectories on and off treatment and linking these to clinical outcomes have created challenges for the health technology assessment of obesity pharmacotherapies globally.

As wider use of pharmacotherapy makes trials challenging to perform, the carefully considered combination and analysis of observational data with clinical trial data will play an important role in overcoming these challenges.