DIFFERENT STRAINS OF CANNABIS CAUSE DIFFERENTPROBLEMS

People who smoke different strains of cannabis show different psychological symptoms, states a study in the April British Journal of Psychiatry. Research suggests a link between cannabis use and psychosis, such as schizophrenia. But cannabis contains a number of chemicals known as cannabinoids, which might have different effects.

The main component of smoked cannabis is a cannabinol known as THC, which is thought to be responsible for the psychosis-like effects of the drug. THC has been shown to raise anxiety levels and psychotic symptoms in healthy people. In contrast, another cannabinol, known as CBD, has been found to lower anxiety and to have antipsychotic properties. The ratio of these two compounds in smoked cannabis varies – there are higher levels of THC in ‘skunk’ or genetically modified strains of the plant. People who use cannabis regularly have been shown to be more prone to psychosis and delusions. No research had examined the link between these effects and the CBD/THC ratio in cannabis until this study used hair analysis to determine levels of THC and CBD in 140 drug users and relate these to measures of psychosis proneness and delusional thinking.

54 people scored positive for cannabis. Both THC and CBD were found in the hair of 26 of them, and THC alone in the hair of 20 others. Participants completed a questionnaire to assess psychosis proneness - for example, experience of hallucinations and delusions, thought disorder, social withdrawal and impulsiveness.

The researchers found significant differences between the 3 groups (THC only, THC+CBD, and no cannabinoid). The THC only group had significantly higher scores for psychosis proneness than the no cannabinoid group and the THC+CBD group. The THC+CBD group also had significantly lower scores for social withdrawal compared with the no cannabinoid group.

Compared with the no cannabinoid group, there were significantly higher scores for delusional thinking in the THC-only group, and a trend for greater scores in the THC +CBD group.

The researchers comment that this study is the first to show that hair analytic techniques can be used to distinguish different groups of cannabis users. The implication is that people who smoke different strains of cannabis have different psychological symptoms.

These findings suggest that smoking strains of cannabis containing CBD in addition to THC may be protective against the psychotic-like symptoms caused by THC alone. However, another explanation of these results might be that pre-existing differences in psychosis proneness between people who use cannabis could draw them to smoke different strains of the drug.

This research highlights the importance of distinguishing between different cannabinoids, and has implications in the debate over the link between cannabis and psychosis.

Morgan C J A and Curran HV (2008). Effects of cannabidiol on schizophrenia-like symptoms in people who use cannabis. British Journal of Psychiatry, 192, 306-307.

For further information contact Dr Celia Morgan, University College London, or Valerie Curran.