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Even though marijuana is known for creating a relaxing state of mind, in some rare situations, smoking the drug can lead to paranoia. In a new study, researchers from Britain set out to uncover how marijuana can cause paranoia. They discovered that the main active ingredient, tetrahydrocannabinol (THC), which calms the body and mind, is also responsible for paranoia.

"The study very convincingly shows that cannabis [marijuana] can cause short-term paranoia in some people," study leader Daniel Freeman, professor of clinical psychology at the University of Oxford in England, said in a university news release reported by Philly. "But more importantly it shines a light on the way our mind encourages paranoia. Paranoia is likely to occur when we are worried, think negatively about ourselves, and experience unsettling changes in our perceptions."

For this study, the team recruited 121 participants between the ages of 21 and 50. All of them had reported using marijuana at least once prior to the study. The researchers administered THC via an injection, which had the strength of one strong joint, to two-thirds of the participants. The remaining one-third received an injection of a placebo drug.

The researchers found that about 50 percent of the people who received the THC injection had paranoid thoughts whereas only 30 percent of the people from the placebo group did. THC was the direct cause of the paranoia in roughly one out of five people. People's paranoid thoughts diminished as the THC left their bloodstream. The researchers noted that other factors did contribute to people's risk of developing paranoia after their injection. People who dealt with low self-esteem, anxiety or worrying were more likely to become paranoid.

"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. Many people have a few paranoid thoughts, and a few people have many paranoid thoughts," Freeman said according to Medical Xpress. "The study identifies a number of highly plausible ways in which our mind promotes paranoid fears. Worry skews our view of the world and makes us focus on perceived threat. Thinking we are inferior means we feel vulnerable to harm. Just small differences in our perception can make us feel that something strange and even frightening is going on."

The study was published in the journal, Schizophrenia Bulletin.