medwireNews: Cannabis may trigger paranoia in vulnerable people by causing negative affect and anomalous experiences, a study shows.
The researchers used the psychoactive ingredient in cannabis - Δ 9-tetrahydrocannabinol (THC) - to trigger paranoia in volunteers who were vulnerable to the experience, reporting at least one paranoid thought in the past month as measured on the Paranoid Thoughts Scale Part B.
A total of 82 participants were randomly assigned to receive 1.5 mL of THC in 10 mL saline or placebo intravenously, after which they underwent a real-life social experience (buying an item from the hospital canteen) and an immersive virtual reality social experience and completed assessments including the State Social Paranoia Scale and the suspiciousness item of the Positive and Negative Symptom Scale.
Participants who received THC were significantly more paranoid during their social experiences than those given placebo, the team reports in Schizophrenia Bulletin.
THC caused a significant increase in negative affect and anomalous experiences, relative to placebo, and this increase was sufficient to account for the entire increase in paranoia. THC also significantly decreased working memory, but this did not have a mediating effect on paranoia.
Other potential mediators, such as external attention, interpersonal sensitivity and threat anticipation, were not affected by THC.
'The clear clinical implication is that reducing negative emotion in patients with delusions, eg, by reducing the tendency to worry, testing out anxious fears, and increasing self-confidence, will lead to improvements in paranoia', say study author Daniel Freeman (University of Oxford, UK) and co-workers.
An additional 39 patients were randomly assigned to receive THC preceded by a brief intervention designed to prepare them for the effects of THC and 'to block the misinterpretation considered central to paranoia.'
Contrary to the researchers' expectations, this intervention did not reduce paranoia, but actually resulted in a nonsignificant increase relative to THC alone, leading them to suggest that the 'awareness condition may have increased sensitivity to paranoid thoughts.'
This was despite some participants in this group saying they were aware that their increased suspicion was caused by THC, and the awareness intervention causing a significant reduction in catastrophising and jumping to conclusions.
'The study indicates that misinterpretations in paranoia do not shift readily simply with provision of an alternative verbal explanation and that unintended consequences could arise from this approach', cautions the team.
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