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Study Sheds Light on Marijuana and Paranoia

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By Peter Russell
WebMD Health News
Reviewed by Rob Hicks, MD

July 17, 2014 -- An in-depth investigation has concluded that people who smoke marijuana are much more likely to have paranoia than people who don't use the drug.

The study also identifies psychological factors that can lead to feelings of paranoia in people exposed to the main psychoactive ingredient in marijuana, THC.

The team of researchers, led by Professor Daniel Freeman, PHD, of the University of Oxford, found that worrying, low self-esteem, anxietydepression, and having a range of unsettling changes in perceptions most likely lead to the feelings of paranoia.

Fearing Harm

A paranoid person is someone who has an unfounded fear that others intend to harm them. Many people have some degree of paranoia. Those who are young, poor, in bad health, contemplating suicide, or using marijuana (also called cannabis) are more prone to have paranoid episodes.

The scientists set out to explore two things:

  • Firstly, does marijuana cause paranoia?
  • Secondly, how does it affect the mind in order to cause paranoia?

Injecting THC

They tested 121 participants between the ages of 21 and 50. All of them had taken marijuana at least once before.

None of the participants had a history of mental illness, and all were screened to rule out relevant health conditions. But all of those taking part said they'd felt paranoid at least once in the previous month.

The volunteers were not invited to smoke joints. Instead, the scientists injected some of them with THC in order to ensure the results were as accurate as possible.

Two-thirds of the participants were given THC, and one-third received a placebo.

The amount of THC given was equal to a strong marijuana joint, and the effects lasted about 90 minutes.

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