Medication can reduce the impact of interfering symptoms, improving the lives of individuals with autism spectrum disorder (ASD) and their families. Although there are no widely-accepted medications for treating the core symptoms of ASD, clinical trials have provided evidence for efficacy and tolerability of medication used for treating comorbid psychiatric conditions. A number of these have a good evidence base, including stimulant medication for the features of attention deficit hyperactivity disorder and risperidone for improving behaviour. Treatment with psychopharmacological agents should only be undertaken after a careful assessment to ensure that any psychiatric symptoms are not the result of underlying physical disorders and to determine which symptoms should be targeted. The aim is to choose and adjust medication that achieves maximum benefit with minimum adverse effects.