Marijuana users less motivated, study says
A study suggests that the use of cannabis can reduce your levels of dopamine, a brain chemical linked to motivation

File photo by EPA/Abir Sultan

MANILA, Philippines – A recently-published study suggests that the long-term use of cannabis can reduce a person’s dopamine levels, a brain chemical linked to motivation, making you less motivated to do things.

Researchers in London used positron emission tomography (PET) brain imaging to look at how much dopamine was produced in the brains of 19 regular cannabis users and 19 non-users of the same age and gender.

The cannabis users in the study first began using the drug between the ages of 12 and 18. All the users experienced psychotic-like syndromes.

The earlier the users started, the lower their dopamine levels were, the researchers found out. The lowest dopamine levels were found in those who met the criteria for cannabis abuse and dependence.

These findings, the researchers said, suggest that the use of cannabis may decrease the brain’s production of dopamine.

It is the first to study effects of cannabis on the dopamine systems of active users, said Dr Michael Bloomfield of Imperial College London, who led the study.

However, these results are contrary to expectations.

Psychosis, a loss of contact with reality, has been linked to higher levels of dopamine. Because previous studies have related cannabis use to psychotic disorders, the researchers expected that the cannabis users would have higher levels of dopamine than normal.

Though the results were unexpected, they were consistent with previous research on addiction, which showed that substance abusers have altered dopamine systems, said Bloomfield.

The results could also explain the supposed ‘amotivational syndrome’ in cannabis users, he added. However, whether or not this syndrome exists is debatable.

Other studies have examined dopamine release in former cannabis users and have reported no difference with people who have not taken cannabis.

This suggests that the effects seen in the study are reversible, the study added.

The study was conducted by scientists at Imperial College London, UCL and King’s College London, was funded by the Medical Research Council and published in the journal Biological Psychiatry. – Cristina Acosta/

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