(From the National Institute for Health, and the National Institute on Drug Abuse)

There are many common myths about marijuana- that marijuana is a benign drug—that it is not addictive (which it is) or that it does not pose a threat to the user’s health or brain (which it does). Recent research funded partly by NIDA and other NIH institutes provides objective evidence that for teens, marijuana is harmful to the brain.

Researchers administered IQ tests to over 1,000 individuals at age 13 and looked at their use of marijuana use at several points as they aged. Participants were again tested for IQ at age 38, and their two scores were compared as a function of their marijuana use. What the research found was that those participants who used marijuana heavily in their teens and continued through adulthood showed a significant drop in IQ between the ages of 13 and 38—an average of 8 points. A loss of 8 IQ points could drop a person of average intelligence into the lowest third of the intelligence range. Those who started using marijuana regularly or heavily after age 18 showed minor declines. By comparison, those who never used marijuana showed no declines in IQ.

This study is the first prospective study to test young people before their first use of marijuana and again after long-term use (as much as 20+ years later). Also those who used marijuana heavily before age 18 showed mental decline even after they quit taking the drug. This finding is consistent with the notion that drug use during adolescence when the brain is still under development can have negative and long-lasting effects on the brain.

While this doesn’t exclude all other factors the declines following marijuana use were present even after researchers controlled for factors like years of education, mental illness, and use of other substances. Researchers also talked to people who knew the study participants (friends and relatives) to ask them about the users’ daily functioning. They reported that heavy marijuana users showed significantly more memory and attention problems such as easily getting distracted, misplacing things, forgetting to keep appointments or return calls, and so on.

This study truly highlights the lasting effects marijuana can have on the teenage brain, which is still in a crucial developmental stage.  It’s up to us as adults to educate teens about the harmful nature of marijuana so that we can align their perceptions of this drug with what science has to show us.

How can I tell if my child has been using marijuana?

Parents should be aware of changes in their child’s behavior, such as carelessness with grooming, mood changes, and deteriorating relationships with fam­ily members and friends. In addition, changes in academic performance, missing classes, loss of interest in favorite activities, change in friends, changes in eating or sleeping habits, and getting in trouble in school could all be related to drug use. Below is a list of specific warn­ing signs for marijuana:

If your child is using marijuana, he or she might:

  • seem unusually giggly and/or uncoordinated
  • have very red, bloodshot eyes or frequently use eye drops
  • have a hard time remembering things that just happened
  • have drugs or drug paraphernalia, including pipes and rolling papers (perhaps claiming they belong to a friend, if confronted)
  • have strangely smelling clothes or bedroom
  • use incense and other deodorizers
  • wear clothing or jewelry or have posters that promote drug use
  • have unexplained lack of money or a surplus

Frequently Asked Questions and Facts about Marijuana:


Marijuana Webinar

The presentation will also clearly define the differences between medical marijuana, decriminalization and legalization and describe their impact on communities. Participants will also learn why community coalitions should care about marijuana use and engage their communities to address the marijuana issue, particularly around formulating messages and developing other effective strategies.

http://www.cadca.org/events/detail/marijuana-science-and-strategies-community-coalitions Just click on “view the webinar recording”