Adherence to a regular medication regimen may be challenging for adults with attention deficit hyperactivity disorder (ADHD). Some report taking psychostimulants on a pro re nata (PRN) basis. This review aims to establish the rate of adherence, and reasons for and consequences of non-adherence to medication for ADHD in adults, and to review literature on PRN dosing of psychostimulants in these patients. A systematic literature search was conducted. Four primary research studies have investigated the rate of adherence to medication in adults with ADHD. Mean adherence rate in two studies ranged from 52% to 87%. A number of possible reasons for poor adherence have been suggested. Prospective studies are needed to further define the rate of adherence and causes of poor adherence. Evidence examining whether differences in adherence affect clinical outcomes is equivocal. Therefore, caution should be applied to the assumption that maximising adherence to regular medication regimens will improve clinical outcomes. Two articles acknowledge that patients take medication on a PRN basis. Studies comparing the effectiveness of a regular and PRN regimen of psychostimulants are needed. If PRN dosing is as effective as a regular regimen, advantages might include enhanced doctor-patient communication, reduced side effects and cost savings.
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