It's drug time - Circadian rhythms and addiction
Like most living creatures, humans have internal biological clocks known as circadian rhythms. These internal cycles synchronize our bodies with the Earth's 24-hour day/night cycle and prepare us for predictable daily events (1). Circadian rhythms regulate a number of bodily functions including temperature, hormone secretion, bowel movements, and sleep (2). Well, recent research suggests that drugs may alter our circadian rhythms, possibly influencing our decisions to take drugs.
Our biological clocks are set by external cues from the environment, called zeitgebers (3). The most familiar to us are light and food. However, research on rats has shown that opiates, nicotine, stimulants, and alcohol also have the ability to alter the phase of circadian rhythms independent of light or food (1). Drug use has long been associated with major disruptions in the human sleep cycle. Cocaine, meth, and MDMA users often go without sleep for days, and these sleep disruptions can continue long after people stop using drugs. In fact, sleep disturbance outlasts most withdrawal symptoms and places recovering addicts at greater risk for relapse (3).
Circadian rhythms could also be the reason why people show 24-hour patterns of drug use. Fluctuations in drug sensitivity, effect, and reward value are believed to be regulated by genes that control circadian rhythms. In fact, a study of urban hospitals found that overdose victims are admitted to hospitals more around 6:30PM than any other time of the day (2).
Researchers are just beginning to explore the relationship between circadian rhythms and drug use. Future understanding of this relationship will help us explain how drug addiction develops and develop better ways to treat it. It's possible that offering specific aspects of treatment as certain point in the circadian rhythm can improve the probability of success.
1. Kosobud, A. E. K., Gillman, A. G., Leffel, J. K., Pecoraro, N.C., Rebec, G.V., Timberlake, W. (2007) Drugs of abuse can entrain circadian rhythms, The Scientific World Journal, 7(S2), 203-212
2. McClung, C.A. (2007) Circadian rhythms, the mesolimbic dopaminergic circuit, and drug addiction, The Scientific World Journal, 7(S2), 194-202
3. Gordon, H.W. (2007) Sleep, circadian rhythm, and drug abuse, The Scientific World Journal, 7(S2), 191-193