A mong the proposed functions of dreaming in human being, the most research supports are mood-regulation, problem-solving, learning, and memory construction. Recent imaging techniques have provided meaningful information on functional neuroanatomy and neurophysiology of REM sleep and dreaming. In addition to serotonin, norepinephrine, and acetylcholine in terms of a reciprocal interaction between the cholinergic REM-ON and aminergic REM-OFF neurons suggested by McCarley and Hobson, dopamine has recently began to think to play a significant role in modulation of dream functions, particularly nightmares. The disinhibition of REM physiology is due primarily to dopaminergic dysfunction, specifically the removal of dopaminergic inhibition on amygdalar sites in dopamin-related syndromes including parkinson disease, REM sleep behavior disorder, and narcolepsy. The disinhibited amygdala yields the affective and personality changes, and the unpleasant dreams associated with PD, RBD, and narcolepsy as well as depression. There is limited data in the literature on drugs and dreaming or dream content even if it is well-known that many antidepressant drugs may cause nightmares or frightening dreams. In this chapter, we review and discuss the effects of medications on dreaming.