- Brains of users were less able to react to feel-good chemical dopamine
- Adds to past research linking marijuana to lethargy and apathy
Smoking cannabis does increase the risk of depression and anxiety, a new study has concluded.
U.S. researchers found the brains of users were less able to react to dopamine - the feel-good chemical that inspires a spirit of get-up-and-go.
The study adds to previous research suggesting marijuana can lead to people becoming withdrawn, lethargic and apathetic.
Danger: The brains of cannabis users were less able to react to the feel-good chemical dopamine
Psychiatrist Dr Nora Volkow, of the National Institute on Drug Abuse in the U.S., used the stimulant Ritalin to see the effect cannabis had on the brain.
Like cocaine, Ritalin raises levels of dopamine in the brain.This made it ideal for the study, published in the journal Proceedings of the National Academy of Sciences.
Of the 48 people in the study, half received the drug - while the other half acted as a control group.
Personality and brain scans showed the cannabis users had significantly blunted dopamine responses compared with the controls who had never taken the drug.
Previous research has suggested a lack of dopamine makes people lazy
This could contribute to drug-craving and negative emotions, a tendency towards depression and anxiety which are hallmarks of cannabis addiction.
Dr Volkow said the phenomenon cannot be unequivocally attributed to reductions in dopamine release.
They believe there is a downstream effect later in the process in an area of the brain called the striatum - the reward and motivation region.
Indeed, last year a study from Imperial College London found that long-term use of cannabis destroys dopamine.
Levels in the striatum - found towards the side of the brain - were lower in regular cannabis users.
Dr Michael Bloomfield, of Imperial College London, said: 'Dopamine is involved in telling the brain when something exciting is about to happen - be it sex, drugs or rock ‘n roll.
'Our findings explain why cannabis has a tendency to make people sit around doing nothing'
Commenting on the new study, the U.S. researchers said: 'Moves to legalise marijuana highlight the urgency to investigate effects of chronic marijuana in the human brain.'
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