Different medications can have significant effects on sleep quality and/or quantity. When prescribing medications it is important to be aware of these possible adverse effects of drugs. Disturbances of the sleep/wake cycle caused by medications can vary and include insomnia, daytime sleepiness, nightmares and changes in the sleep architecture. Psychotropic drugs are well known to have an effect on the sleep/wake cycle, but there is only limited information about the sleep effects of nonpsychotropic medications. Cardiovascular drugs, especially beta-blockers, which are widely used drugs, often change the sleep architecture and cause nightmares and insomnia. Both of these effects can be a potential source of noncompliance. Because of the complicated relationship between sleep, nocturnal asthma and antiasthmatic agents, the appropriate dosage and timing of medications should always be considered. Patients with Parkinson's disease often experience disrupted sleep due to their disorder and the adverse effects of anti-parkinsonian medications.