A new study led by Oxford Professor Daniel Freeman claims to have definitively shown that cannabis can cause short-term paranoia in “some people.”

More importantly however, the study also identifies the ways in which our minds encourage paranoia. Professor Freeman, of University College, concluded that “paranoia is likely to occur when we are worried, think negatively about ourselves, and experience unsettling changes in our perceptions.”

The study, published in the journal Schizophrenia Bulletin, is the first to determine the psychological factors that can result in feelings of paranoia in cannabis users, and confirms the findings of investigations dating back to the 1930s, as well as the widely-held suspicions of centuries of users.

The research involved Freeman’s team tested the mental responses of 121 participants between the ages of 21 and 50, all of whom had taken cannabis at least once before and none of whom had any history  of mental illness or health condition, while they were placed in tests of “excessive suspiciousness.” These including real-life social situations, a virtual reality simulation, self-report questionnaires and clinical interviews.

Two-thirds of the participants were injected with the main psychoactive ingredient in cannabis, THC (Δ9-tetrahydrocannabinol), while a third received a placebo. The dose of THC was equivalent to a strong joint, with the chemical having effect for 90 minutes.

Half of the participants who took THC reported paranoid thoughts, compared to 30% of those who took the placebo.

The drug also caused a range of other psychological effects in those who took it, ranging from anxiety, worry, lowered mood, and negative thoughts about the self, to various changes in perception such as sounds being louder than normal and colours brighter, thoughts echoing, altered perception of time, and poorer short-term memory.

Commenting on the findings, Professor Freeman explained that “paranoia is likely to occur when we are worried, think negatively about ourselves, and experience unsettling changes in our perceptions.

“Paranoia is excessive thinking that other people are trying to harm us. It’s very common because in our day-to-day lives we have to weigh up whether to trust or mistrust, and when we get it wrong – that’s paranoia. The study identifies a number of highly plausible ways in which our mind promotes paranoid fears.

He continued, “The study provides a great deal more information about the immediate effects of cannabis, but it did not investigate clinically severe disorder. The results don’t necessarily have any implications for policing, the criminal justice system, or legislation. It tells us about the little discussed paranoid-type fears that run through the minds of so many people from time to time.

“The implication is that reducing time spent ruminating, being more confident in ourselves, and not catastrophizing when unusual perceptual disturbances occur will in all likelihood lessen paranoia.”

Meanwhile, a first year Jesus geographer agreed that the ill-effects of paranoia from cannabis can be lessened by a positive outlook, commenting that “being paranoid would be unpleasant if I wasn’t extremely comfortable on a sofa or sunbathing.”

However, he also told Cherwell, “these findings have nevertheless seriously made me question the efficacy of bunning, especially since I hear that second year is really tough.”