A sustained-release drug is a formulation that releases its active ingredient gradually, so one dose lasts longer than an immediate-release version of the same medicine.
In Ireland and the UK these are often labelled modified-release, prolonged-release or XL. Many long-acting ADHD medicines use this approach. Lisdexamfetamine lasts a long time for a different reason: the body converts it into its active form gradually.
Fewer doses mean fewer chances to forget, which matters with ADHD. The effect also rises and falls more evenly than with several short-acting doses.
Sustained-release tablets and capsules usually must not be crushed or chewed, because that can release the whole dose at once. Check the leaflet before splitting or opening anything.