A new study conducted in association with The University of Oxford and King’s College London has found a definitive link between cannabis use and feelings of paranoia in vulnerable individuals.

Professors Daniel and Jason Freeman have today published their findings in Schizophrenia Bulletin, following research conducted on 121 volunteers, all of whom had experienced marijuana at least once before.

The study focused on the effects of ?9-tetrahydrocannabinol (THC): cannabis’ main psychoactive component. Seventy percent of the volunteers were given a small intravenous dose of THC (the equivalent of a strong joint), while the remaining 30 percent made up a placebo group, receiving a shot of saline.

Commenting on their findings in the Guardian, the professors reported that half of those given THC experienced paranoia, compared with 30 percent of the placebo group. “That is, one in five had an increase in paranoia that was directly attributable to the THC,” they said.

Researchers acknowledged that these effects were limited to a minority of their respondents and acknowledged the positive effects of cannabis usage, including the alleviation of chronic pain. “Clearly cannabis doesn’t cause these problems for everyone, and the suspiciousness wore off as the drug left the bloodstream,” they said. The study also indicated that THC is not addictive.