Light and dark as a "drug".
Wirz-Justice
A
A
D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D006801:Humans; D008027:Light; D019964:Mood Disorders / Q000628:therapy*; D010507:Periodicity; D010789:Phototherapy; D010870:Pineal Gland / Q000502:physiology; D011619:Psychotropic Drugs; D012621:Seasons
D011619:Psychotropic Drugs