Heavy cannabis use may affect motivation–study

In a novel study, scientists at Imperial College London, UCL and King’s College London have gathered convincing evidence that use of cannabis, the most common illicit drug makes people less motivated.

According to experts, prolonged use of the drug destroys dopamine, the chemical in the brain’s striatum, that is involved in novelty-related decision making and motivation.

The study found chronic cannabis users who began smoking at a younger age produced less dopamine than those who abused the street drug at the later stage.

Lead author of the study, Dr Michael Bloomfield, of Imperial College London stated, “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. The results weren’t what we expected but tie in with previous research on addiction which has found substance abusers have altered dopamine systems.”

Study details
In order to determine whether early exposure to cannabis can turn users into unmotivated slackers the researchers carried out a study. They performed positron emission tomography (PET) scans on the brains of 38 people of matching sex and age.

The study subjects included 19 young cannabis users who smoked pot regularly and 19 non users. The cannabis users were heavily into marijuana and had begun abusing the drug at an early age, some as young as 12 years.

All the cannabis users in the study had experienced psychotic-like symptoms (strange sensations, such as strange sensations or having feelings of paranoia) while smoking pot.The investigators anticipated their dopamine production to be elevated since increased production of the chemical has been linked with psychosis. However, to their surprise, they found the opposite effect.

Experts attribute drug use to the difference in dopamine levels. Users who met the diagnostic criteria for chronic cannabis abuse displayed the lowest dopamine levels, an indication that it could be a marker of severe addiction.

Earlier research has revealed that the risk of mental illnesses such as schizophrenia is more pronounced in chronic cannabis users.

Bloomfield explained, “It has been assumed that cannabis increases the risk of schizophrenia by inducing the same effects on the dopamine system that we see in schizophrenia, but this hasn’t been studied in active cannabis users until now.

“Although we only looked at cannabis users who have had psychotic-like experiences while using the drug, we think the findings would apply to cannabis users in general, since we didn’t see a stronger effect in the subjects who have more psychotic-like symptoms. This needs to be tested though.

“It could also explain the ‘amotivational syndrome’ which has been described in cannabis users, but whether such a syndrome exists is controversial.”

The study is published in the journal Biological Psychiatry.

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