Cannabis Use Linked With 'Substantial Adverse Effects,' Says NIDA Review

July 2, 2014

Use of marijuana is linked with “substantial adverse effects,” according to a review article published in the June 5 New England Journal of Medicine. 

These adverse effects include addiction and impairments in cognitive and motor function, wrote Nora D. Volkow, MD, and colleagues from the National Institute on Drug Abuse (NIDA) in Bethesda, Maryland. In particular, adolescents’ developing brains may experience long-lasting changes in function due to repeated exposure to marijuana. 

In the article, Dr. Volkow and colleagues said that the question of marijuana’s harmfulness has been subject to “heated debate,” but that a literature review reveals areas with strong evidence of adverse health effects. 

  • Approximately 9% of people who experiment with marijuana become addicted
  • Cannabis withdrawal syndrome makes cessation of the drug difficult and contributes to relapse
  • People who begin using marijuana as adolescents are two to four times more likely to become dependent on the drug than those who began as adults
  • Marijuana has negative effects on functional connectivity of the brain, particularly if use begins in adolescence or young adulthood
  • Marijuana intoxication can have detrimental consequences, such as motor-vehicle accidents 

However, although marijuana has been linked to increased risk of mental illnesses such as anxiety, depression, and psychosis, “it is inherently difficult to establish causality in these types of studies because factors other than marijuana use may be directly associated with the risk of mental illness,” the authors write. 

Use of marijuana is under scrutiny as a risk factor for lung cancer, but the evidence is not definitive at this point. The authors also question whether some older studies on the effects of marijuana use remain valid, as the potency of marijuana has steadily increased during the past three decades. 

Dr. Volkow and colleagues call for more research on how government policies can influence public health outcomes and how to help sick people take advantage of the medical benefits of marijuana while mitigating the risks inherent in its use. Legalization of marijuana will likely lead to more widespread exposure and “negative health consequences” for those who use the drug, the researchers noted

—Lauren LeBano 


1. Volkow NJ, Baler RD, Compton WM, Weiss SRB. Adverse health effects of marijuana use. N Engl J Med. 2014;370(23):2219-2227.