[Circadian rhythmicity and addiction]

The chronobiological aspects of addiction constitute a recently developed field of study that has obtained interesting data from both basic and clinical research. Drug consumption has a negative effect on the expression of circadian rhythmicity, since it produces a flattening of the functions and a delay of maximal values, and can even cause a state of desynchronization of endogenous control. Moreover, it has been shown that the clock-genes Clock and Per2 are associated with vulnerability to addiction, the first gene directly regulating dopaminergic activity in the reward system and the second participating in the sensitivity to and abstinence from drugs. The evening circadian typology has also been proposed as an individual difference to be taken into account as a risk factor in the development of drug addiction. Finally, the reorganization of circadian rhythmicity with regular daily schedules adjusted to the cycle of light-darkness, exposure to natural or artificial light, and the administration of melatonin may be useful strategies in the treatment of drug addictions.