December 6, 2021

I, Science

The science magazine of Imperial College

Taking a wide view on this cannabis talk at the Imperial Festival 2014 ...


The controversial topic of cannabis has occupied the headlines recently, as a wave of legalisation sweeps through the US. The coverage has been accompanied by a lively to-and-fro about the long term effects of the drug. At the core of this debate is a simple question: “If cannabis is so dangerous, why is it that everybody I know who uses it is fine?”

Dr Michael Bloomfield set out to tackle this question and explain some of his own research in the talk ‘Cannabis and the Brain’, part of the Friday night programme at the Imperial Festival. Bloomfield began by taking the audience on a whistle-stop tour of the drug’s history, starting with its importation to Europe from Indochina in the 19th Century. Explorer-come-scientist Jacques-Joseph Moreau was the first to take an empirical approach to studying the effects of cannabis. His interest in the plant did not stop there, however, and he went on to establish the first club in Paris to host recreational users of the drug.

Today, almost half of young people have used cannabis in the last month. In the US, 1 in 20 will abuse it at some point during their life. Whilst researchers agree that regular use is a risk factor for mental illness, the degree of this risk and the possible positive effects of the drug are still a matter of contention.

One broad category of mental illness is psychosis, which includes illnesses such as schizophrenia. Most psychiatrists believe that cannabis is a risk factor for psychosis but there’s a great deal of disagreement over the extent. The increasingly sophisticated understanding of risk level will help inform users, and there’s also research being done into personality types that are known to be high risk and where the user may suffer unpleasant hallucinatory experiences, especially when first trying the drug.

Bloomfield’s research has focused on differing effects of the two active components: Tetrahydrocannabinol (THC) and Cannabidiol (CBD). In hashish and herbal cannabis these components come in roughly equal quantities, however, most of the marijuana sold in the UK comes in the form of skunk, which is grown hydroponically indoors. In skunk, the THC component dominates.

In controlled experiments, almost all subjects injected with pure THC developed psychotic symptoms for the duration of the high. The same was not true for those injected with a THC/CBD mix. In fact, CBD is now being used to actually treat psychosis.

Bloomsfield also used PET scanning to measure the levels of dopamine in the brains of regular cannabis users and found that people with low dopamine were likely to abuse cannabis. This follows a similar trend in the abuse of other drugs and suggests that users may in fact be attempting to self-medicate.

Dopamine has a strong role in motivation, leading to headlines suggesting that “Smoking cannabis does make people lazy,” and Bloomfield’s research found a strong relationship between apathy and dopamine levels.

What do these various discoveries tell us about the overall health impact of cannabis and how should this affect public policy and personal choices? Bloomfield steered clear of making recommendations but indicated support for Dr David Nutt’s infamous study that compared the negative impacts of several recreational drugs and found cannabis to be well below tobacco and alcohol. He finished a stimulating talk by calling for more research into the less well studied areas of recreational drug interactions, for example, how cannabis interacts with tobacco, alcohol, other party drugs and caffeine.

The talk ‘Cannabis and the Brain’ took place on 9 May 2014 at Imperial College London as part of the Imperial Festival.


IMAGE: Wikicommons