Brain’s Motivation Blunted!
Long-term cannabis users tend to produce less dopamine, a chemical in the brain linked to motivation. Dopamine levels in a part of the brain called the striatum were lower in people who regularly smoke cannabis, especially those who began taking the drug at a younger age. This explains why some cannabis users appear to lack motivation to work or pursue their normal interests. The lowest dopamine levels were seen in users who met diagnostic criteria for cannabis abuse or dependence, raising the possibility that this measure could provide a marker of addiction severity.
Biological Psychiatry, July 2013