Psychostimulants are a broad class of sympathomimetic drugs that include drugs of abuse, such as illegal substances, as well as therapeutic drugs, such as methylphenidate and modafinil. The common effect of psychostimulants is to improve motivation, mood, movement, energy, wakefulness, arousal, anorexia and attention. Methylphenidate and modafinil are psychostimulants used in the treatment of attention deficit hyperactivity disorder and narcolepsy. They have also been found to be effective for treating certain cognitive disorders that result in secondary depression or profound apathy, obesity, cancer-related fatigue as well as in specific treatment-resistant depressions as an augmentation therapy with antidepressants. Psychostimulants are also used in an non-medical manner, such as cognitive and/or performance enhancers in healthy population. However, the most limiting adverse effect of psychostimulants is their vulnerability to psychological and physical dependence. Therefore, the abuse and misuse of stimulants, including methylphenidate and modafinil, for the purpose of neuroenhancement is an issue of concern throughout the world including Korea. Although several recent studies have reported on the cognitive and performance enhancement effects of methylphenidate and modafinil in healthy population, psychostimulants should be administered with discretion in the light of their potential adverse effects and the lacks of long-standing efficacy.