Circadian rhythms prepare organisms for predictable events during the Earth's 24-h day. These rhythms are entrained by a variety of stimuli. Light is the most ubiquitous and best-known zeitgeber (time-giver), but a number of other cues have been identified, including food, social cues, and locomotor activity. Given the prevalence of zeitgebers, it is not surprising that genes capable of circadian timing functions are located in most organs and tissues. Recent evidence argues strongly that drugs of abuse also directly entrain circadian rhythms. We review data showing that the entrainment abilities of drugs of abuse can be independent of the light-dark cycle and the suprachiasmatic nucleus, do not depend on direct locomotor stimulation, and are shared by a variety of drug classes. We suggest that such drug-entrained rhythms reflect variations in underlying neurophysiological states that contribute to demonstrated daily variations in drug metabolism, tolerance, and sensitivity to drug reward. These rhythms may also produce daily periods of increased motivation to seek and take drugs. In short, circadian entrainment to the timing of drug administration may be a contributing factor in drug abuse, addiction, and relapse.
- Circadian rhythm
- Drug abuse
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Environmental Science(all)