Methylphenidate extended release capsules. What is this medication? METHYLPHENIDATE (meth il FEN i date) treats attention-deficit hyperactivity disorder (ADHD). It works by improving focus and reducing impulsive behavior. It belongs to a group of medications called stimulants.There are several brands of ‘slow-release’ methylphenidate tablets or capsules (they may also be referred to as ‘modified-release’ or ‘XL’). These release some of the methylphenidate straight away but release the rest slowly throughout the day. For this reason, they can be taken less often .