Drug-induced Dopamine Dip

 5 July 2013   Research News

3vnzaly1Scientists reveal how cannabis affects the brain

The research of a CSC Clinical Research Fellow has recently caught the attention of the Daily Mail, New York Daily News, The Huffington Post and CBS.

Michael Bloomfield, who will soon complete his PhD under Oliver Howes (Psychiatric Imaging Group), studied dopamine levels in the brains of 19 regular cannabis users, who experienced psychotic-like symptoms while smoking the drug. He was surprised to discover that dopamine levels were lower in the striatum of these regular cannabis users when compared to non-users. The finding runs contrary to the research group’s expectation of higher levels.

While cannabis use is associated with an increased risk of mental illness, how the drug manifests at the molecular level in the brain has not been fully elucidated. As Oliver Howes explains, “It’s long been thought, but never directly tested, that the link between cannabis use and psychosis comes about through changes in dopamine levels.” The people studied by Bloomfield didn’t have schizophrenia, but experienced altered perceptions of reality, such as paranoia, while consuming the drug.

The main finding of the study, published in Biological Pyschiatry, was that regular and current cannabis users have a reduced capacity for dopamine synthesis in the striatum, an area of the brain that controls working memory and plays a role in reward. “Our findings of lower dopamine production in cannabis users may help explain why regular users find it hard to quit,” clarifies Howes.

As Bloomfield explains, “We found quite a strong relationship between the amount of cannabis people were smoking and the lowering of dopamine levels.” This would suggest that cannabis is causing the reduction in dopamine production in the brain. Additionally, starting younger seems to further depress dopamine levels. However, related studies in ex-cannabis users didn’t find any changes in dopamine levels within the striatum, so perhaps the effects may be reversible.

The scientists discuss in the paper how their findings might help to explain the ‘amotivational syndrome’ associated with regular cannabis use, which led to the Daily Mail headline ‘Smoking cannabis really DOES make people lazy because it affects the area of the brain responsible for motivation.’ An article published in Imperial College News reveals a lively discussion following the published research featuring claims that scientists are trying to ‘demonise’ cannabis.

Bloomfield responds, “We’re not trying to demonise cannabis. We want to find out what effects it has on the brain. If we did a study measuring vitamin A levels in people who eat lots of carrots every day, we wouldn’t be trying to demonise carrots. We think it’s important to study cannabis because 1 in 3 people in the UK try the drug and because large studies have shown that using cannabis regularly increases the risk of mental health problems.”


Reference: Bloomfield et al, Dopaminergic function in cannabis users and its relationship to cannabis-induced psychotic symptoms. Biological Psychiatry, 2013.