Drug absorption is the process by which a medicine moves from where it was taken, such as the stomach or gut, into the bloodstream so it can start working.
How fast and how much is absorbed depends on the medicine, its formulation and the person. Food, stomach acid and other medicines can all change it.
This explains some everyday experiences with ADHD medication. With certain products, some people notice a dose takes longer to start working after a large meal. Some find a long-acting medicine feels different on days when they eat at different times. Those are absorption effects, and they're worth mentioning at a review.
The patient information leaflet says whether a medicine should be taken with or without food. Follow that rather than general advice online.