Circadian entrainment by food and drugs of abuse

•Circadian rhythms are physiological and behavioral rhythms that have a daily cycle.•The most well-known circadian rhythm is the rest/activity cycle, entrained by transitions to daylight and darkness.•Light-independent circadian rhythms are entrained by food; social, sexual or stressful events; and drugs of abuse.•This suggests circadian rhythms that organize behavior and physiology around motivationally significant events.•Rhythms entrained by drugs of abuse may play a role in drug seeking, taking, addiction and relapse.