"The [endo] cannabinoids produce psychological states that closely parallel several experiences described as being related to the runner’s high. Compared with the opioid analgesics, the analgesia produced by the endocannabinoid system is more consistent with exercise induced analgesia. Activation of the endocannabinoid system also produces sedation, anxiolysis, a sense of wellbeing, reduced attentional capacity, impaired working memory ability, and difficulty in time estimation. This behavioural profile is similar to the psychological experiences reported by long distance runners."
Dietrich, A and McDaniel, W, "Endocannabinoids and exercise," British Journal of Sports Medicine (Middlesex, United Kingdom: British Association of Sport and Exercise Medicine, October 2004), Volume 38, pp. 539-540.
http://www.ncbi.nlm.nih.gov/p…
