Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started
My Medicine

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Brain & Nervous System Health Center

Font Size

Study Sheds Light on Marijuana and Paranoia

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, anxiety, depression, 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.

Today on WebMD

nerve damage
Learn how this disease affects the nervous system.
senior woman with lost expression
Know the early warning signs.
woman in art gallery
Tips to stay smart, sharp, and focused.
medical marijuana plant
What is it used for?
senior man
boy hits soccer ball with head
red and white swirl
marijuana plant
brain illustration stroke
nerve damage
Alzheimers Overview
Graphic of number filled head and dna double helix