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New Research Raises Concerns About the Dangers of Marijuana Use

Whatever your personal position on the subject of marijuana legalization, whether for medical or recreational use, a growing body of research reveals concerns over the potential harms caused by cannabis.

The concerns are more than academic. With increasing public support (varying by demographic cohorts) for legalized marijuana, and 10 states legalizing recreational marijuana and 33 states where medical marijuana use is legal, the cannabis movement is just gaining steam.

A new Pew Research Center report shows that 6 in 10 Americans (62 percent) say marijuana should be legal. Millennials support legalized marijuana more than any other group (74 percent), followed b Gen Xers at 63 percent, and Baby Boomers at 54 percent. The Silent Generation shows the least support for legalized marijuana at 39 percent, although they have shown greater support in the last year.

Long-Term Use of Cannabis of Cannabis-Based Drugs Impairs Memory

Researchers from Lancaster and Lisbon Universities studied the effects of a cannabidiol drug in mice and found disturbing results:

  • Long-term cannabis exposure impairs memory and learning in the animals.
  • Brain imaging studies showed functional impairment in key brain areas involving learning and memory.
  • Underlying the drug’s negative effects on memory may be the fact that long-term exposure causes impairment in brain regions involved in learning and memory to communicate with each other.  

Researchers noted that while cannabis-based therapies can be effective in both treating symptoms of chronic diseases such as epilepsy and multiple sclerosis and in improving the quality of life for patients, much more should be learned about the side effects of these drugs so that interventions can be developed to minimize them.

There is also a marked difference in cannabis used for medical reasons versus non-medical use. While prolonged cannabis intake may re-establish equilibrium in those with certain disease conditions (such as epilepsy or multiple sclerosis), but long-term cannabis use creates marked imbalances in healthy individuals.

Vaping Cannabis Produces Greater Negative Effects Than Smoking the Same Dose

In a small study of infrequent cannabis users, researchers at Johns Hopkins University found that vaping cannabis results in increased rates of short-term anxiety, distraction, memory loss and paranoia compared to smoking the same doses. Researchers said that because of increased legalization of cannabis, they wanted their study to be more representative of infrequent or first-time cannabis users who may not understand or be able to predict the drug’s effects. For example, infrequent cannabis vapers should be cautious about how much cannabis they vape, and avoid driving for several hours after use. They should also be mindful of the side effects they may experience, including anxiety, nausea, vomiting, and hallucinations.

Tests also showed vapers of cannabis demonstrated more functional impairment in driving and performing everyday tasks than cannabis smokers. Researchers also noted that these effects were observed in infrequent cannabis users and may not apply to routine cannabis users, who may have developed drug tolerance and may also be better able to regulate their dose. The study, published in JAMA Network Open, was funded by the Substance Abuse and Mental Health Services Administration (SAMHSA).

More Than Half of People Using Marijuana for Chronic Pain Drive While High

Another concerning finding is highlighted in a study conducted by researchers at the University of Michigan’s Addiction Center. According to their study, funded by the National Institute on Drug Abuse (NIDA), and published in the journal Drug & Alcohol Dependence, more than half of medical cannabis users taking the drug for chronic pain say they’ve driven while high within 2 hours of using at least one time in the last 6 months.

Michigan, with nearly 270,000 medical marijuana users (as of May 2018), is second only to the state of California in terms of highest number of medical marijuana patients in a state.

Lead author, Erin E. Bonar, Ph.D., calls the study results “troubling,” and said the safest strategy “is to not drive at all on the day you use marijuana.” Fifty-six percent of study participants said they drove a motor vehicle within 2 hours of using marijuana. Alarmingly, 51 percent said they drove “a little high,” and 21 percent said they drove “very high.”

The dangers of medical marijuana use to driving include:

  • Reaction time and coordination may be slowed down.
  • Drivers could have a harder time reacting to the unexpected.
  • In a risky situation, such drivers could be more likely to be involved in a crash, because their response time wasn’t quick enough.

Bonar indicated that chronic daily users might have even longer-lasting effects of the marijuana lingering in their system. The study was conducted before Michigan became the 10th state in the nation legalizing the recreational use of marijuana (November 2018). In an email, Bonar said they followed these study participants for 2 years and have “just scratched the surface of the wonderful information they provided us,” adding that there will be more papers forthcoming as her group analyzes the data.

Cannabis Use Appears to Increase Risk of Prescription Opioid Use Disorder

A 2017 study published in The American Journal of Psychiatry found that, rather than decreasing risk, cannabis use appears to increase the risk of developing non-medical prescription opioid use and opioid use disorder (OUD) in the U.S. Researchers assessed prospective associations between cannabis use at wave 1 and nonmedical prescription opioid use and opioid use disorder at wave 2. Researchers also did corresponding analyses of adults with moderate or more severe pain, along with nonmedical opiate use at wave 1.

Noting the long-standing controversy over the extent to which cannabis use predisposes subsequent use of opioids and other substances of abuse, researchers said their findings showed “that cannabis use, even among adults with moderate to severe pain, was associated with a substantially increased risk of nonmedical prescription opioid use at 3-year follow-up.” They also said that while the great majority of cannabis users did not go on to initiate/increase nonmedical use of opiates, caution should be used in any ongoing cannabis policy discussions and clinical debate on authorizing medical marijuana to reduce nonmedical use of prescription opiates and combat opioid overdose deaths.


Rense, S. (2018, November 7). Here are all the states that have legalized weed in the U.S. Esquire. Retrieved from

Hartig, H., & Geiger, A. (2018, October 8). About six-in-ten Americans support marijuana legalization [blog post]. Retrieved from

Mouro, F.M., Ribeiro, J.A., Sebastiao, A.M. (2018, July 10). Chronic, intermittent treatment with a cannabinoid receptor agonist impairs recognition memory and brain network functional connectivity. Journal of Neurochemistry, 147(1): 71-83. Retrieved from

Vaping cannabis produces stronger effects than smoking cannabis for infrequent users [release]. (2018, December 4). Retrieved from

Spindle, T.R., Cone, E.J., Schlienz, N.J, Mitchell, J.M., Bigelow, G.E., Flegel, R., Hayes, E., Vandrey, R. (2018, November 30). Acute effects of smoked and vaporized cannabis in healthy adults who infrequently use cannabis: A crossover trial. JAMA Network Open, 1(7). Retrieved from

Abraham, S. (2019, January 10). More Than Half of People Taking Cannabis for Chronic Pain Report Driving While High [blog post]. University of Michigan Mental Health Lab. Retrieved from

Olfson, M., Wall, M.M., Liu, S.M., Blanco, C. (2017). Cannabis Use and Risk of Prescription Opioid Use Disorder in the United States. The American Journal of Psychiatry, 175(1): 47-53. Retrieved from

New Research Raises Concerns About the Dangers of Marijuana Use

Suzanne Kane

Suzanne Kane is a Los Angeles-based writer, blogger and editor. Passionate about helping others live a vibrant and purposeful life, she writes daily for her website, She is a regular contributor to Psych Central. You can reach her at

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APA Reference
Kane, S. (2019). New Research Raises Concerns About the Dangers of Marijuana Use. Psych Central. Retrieved on September 30, 2020, from
Scientifically Reviewed
Last updated: 19 Jan 2019 (Originally: 20 Jan 2019)
Last reviewed: By a member of our scientific advisory board on 19 Jan 2019
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