THC (Δ9-tetrahydrocannabinol), active psychoactive ingredient in cannabis, can cause short-term paranoia, according to a new study by the Oxford University.
Researchers said that worrying, low self-esteem, anxiety and changes in perception most likely lead to feelings of paranoia in cannabis users.
"..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," Professor Daniel Freeman said in a statement.
This is the first study to determine psychological factors that can result in feelings of paranoia in cannabis users.
For the study, the researchers tested 121 participants' paranoia levels through tests of excessive suspiciousness including real-life social situations, a virtual reality simulation, self-report questionnaires and clinical interviews.
All the participants, in the age group of 21-50 years, consumed cannabis at least once before and did not have a history of mental illness.
Researchers found that all participants reported mistrustful thinking in their day to day lives.
In the second experiment, two thirds of the participants were injected with the principal psychoactive constituent of cannabis and one-third were injected with a placebo.
Researchers found that THC increased the occurrence of paranoia in the participants. About half of the participants experienced paranoid thoughts with THC when compared to 30 percent on placebo.
Plus, THC-use also led to other psychological effects: anxiety, worry, lowered mood, negative thoughts about the self, 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.
"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," said Freeman.
The finding is published in the journal Schizophrenia Bulletin.
