Bad news, stoners – weed doesn't just ruin your sperm, but there might be some truth in the old superstition that getting stoned makes you paranoid. A study published today in the aptly-named Schizophrenia Bulletin claims that THC, the main psychoactive component in marijuana, really does trigger paranoid thoughts in vulnerable people. 

"Certainly many people use cannabis without adverse effects, and indeed with plenty of very pleasant ones," write Professor Daniel Freeman and science writer Jason Freeman in the Guardian. "Moreover, there is evidence that cannabis can bring real medical benefits, for example in alleviating chronic pain. But there is also known to be a link between cannabis and paranoid thoughts."

Their team of researchers from the University of Oxford, the Institute of Psychiatry at King's College London, and the University of Manchester discovered "clear results" that THC caused paranoid thoughts. In the study, 121 volunteers were selected and randomly administered with either a 1.5mg dose of THC or a placebo.

50% of the patients given THC reported paranoid thoughts, compared with 30%  of the placebo group. The THC also produced effects such as anxiety, worry, lowered mood and negative thoughts about the self. 

"Clearly cannabis doesn’t cause these problems for everyone," the study authors clarify. "And the suspiciousness wore off as the drug left the bloodstream. But the study does show that paranoia isn’t tenuously linked to THC: for a significant number of people, it’s a direct result."

So, next time you meet a really friendly guy in an Eastern European hostel, remember that there's a chance you'll end up in your room crying "I should never have come to Bratislava" after you split the doobie he's offering.