People who smoked marijuana regularly as teenagers remembered fewer words as they entered middle age, according to a new study published online by JAMA Internal Medicine.
For this study, researchers randomly selected more than 5,000 young adults from 18 and 30 and followed up with them at varying points over 25 years. At the end of the 25 years, there were more than 3,400 participants still in the study. Their cognitive function was measured using standardized tests of verbal memory, processing speed and executive function.
The study found current marijuana use was associated with poorer verbal memory and processing speed, and lifetime exposure to marijuana was associated with worse performance in all three areas of cognitive function.
Although past exposure to marijuana was associated with worse verbal memory, it does not appear to affect other domains of cognitive function.
It is unclear whether there are long-term effects on memory from occasional marijuana use earlier in life and whether there is an impact on other areas of cognitive function.
"In this study, there are as much women as men, as much black as white, as much lower education as higher education," said Dr. Reto Auer, one of the study's authors.
"It provides a better sense of what the association is in the overall population."
The authors of the review put forward several possible explanations for the association between long-term marijuana use and worse verbal memory.
“We know marijuana has been associated with underlying measures that are linked in the hippocampus. Structural changes in the hippocampus could explain these associations, where you would find that people have a problem retaining words that would not impact on other domains of cognition,” Dr Auer said.
(Reto Auer, MD, MAS1. “Association Between Lifetime Marijuana Use and Cognitive Function in Middle Age: The Coronary Artery Risk Development in Young Adults.” JAMA Intern Med. Published online February 01, 2016.)
Commenting on the findings for Medscape Medical News, Nadia Solowij, PhD, associate professor, School of Psychology, University of Wollongong, New South Wales, Australia, described the study as a “welcome addition to the literature.”
She told Medscape Medical News that longitudinal studies of the use of cannabis are rare and that the current investigation confirms previous associations between use of the drug and poorer cognitive function.
Dr Solowij noted that although the participants were middle-aged, the impairment of memory function “does not appear to be age-related, rather, related to the cumulative exposure to cannabis, indicating that greater cannabis use at any age has the potential to impair cognitive functioning.”
A remaining matter for debate is whether memory dysfunction associated with cannabis use can resolve following prolonged drug abstinence. “The evidence for recovery remains uncertain and mixed from the sparse literature addressing this important question,” Dr Soliwij concluded.
(Liam Davenport. “Marijuana Use Impairs Verbal Memory.” Medscape. February 08, 2016.)
"The public health challenge is to find effective ways to inform young people who use, or are considering using, marijuana about the cognitive and other risks of long-term daily use," wrote authors Wayne Hall of the Center for Youth Substance Abuse Research at the University of Queensland in Australia and Michael Lynskey of the National Addiction Centre at King's College London.
"Young adults may be skeptical about advice on the putative adverse health effects of marijuana, which they may see as being overstated to justify the prohibition on its use," the authors write. "More research on how young people interpret evidence of harm from marijuana and other drugs would be useful in designing more effective health advice."
I'm sure every advocate for the recreational legalization of marijuana will dispute this new research; however, as one of the few long-term cannabis use studies about the effects on the brain, this information should throw up red flags. We must give people – especially youth at risk – critical, honest information about all vices, including the use of marijuana. And, yes, I acknowledge drinking alcohol and smoking cigarettes as vices.
I don't wish to argue about the potential uses for medical marijuana. I see medical marijuana as a separate issue. My opinion here is restricted to recreational use.
Good news has arrived. According to research (2015) from The University of Texas at Austin School of Social Work, since 2002, the proportion of adolescents reporting marijuana use has decreased, and more younger adolescents report strong disapproval of marijuana use initiation (despite recent legalization in some states).
(Christoper P. Salas-Wright et al. “Trends in the disapproval and use of marijuana among adolescents and young adults in the United States: 2002–2013.” The American Journal of Drug and Alcohol Abuse. Volume 41. 2015.)
In addition, 2014’s Monitoring the Future survey of drug use and attitudes among American 8th, 10th, and 12th graders (National Institute on Drug Abuse) continued to show encouraging news about youth drug use, including decreasing use of alcohol, cigarettes, and prescription pain relievers; no increase in use of marijuana; decreasing use of inhalants and synthetic drugs, including K2/Spice and bath salts; and a general decline over the last two decades in the use of illicit drugs.
However, the survey highlighted growing concerns over the high rate of e-cigarette use and softening of attitudes around some types of drug use, particularly decreases in perceived harm and disapproval of marijuana use.
And, a study by the Johns Hopkins Bloomberg School of Public Health researchers published in the journal Drug and Alcohol Dependence says that marijuana use is significantly greater than the use of other illegal drugs, with 40 percent of teens in 2013 saying they had ever smoked marijuana.
Although research finds marijuana less addictive than alcohol or tobacco and symptoms of marijuana withdrawal tend to be shorter-lived, a study on teens (2014) suggests marijuana dependence (notice I didn't say “addiction”) may be a bigger problem than many people realize.
For the small-scale study, researchers evaluated 127 teenagers being treated at an outpatient substance use disorder clinic in Boston.
The study by the Massachusetts General Hospital in Boston showed that of the 90 teens who cited marijuana as the substance they used most frequently, 76 met criteria for cannabis dependence – including increased tolerance of cannabis and unsuccessful efforts to cut back or stop using despite medical or psychological problems exacerbated by cannabis. And 36 of the 90 experienced anxiety, irritability, depression, or other symptoms considered hallmarks of drug dependence.
(David Freeman. “Marijuana Study Raises New Concerns About Pot Addiction In Teens.” Huffington Post. September 05, 2014.)
Finally, to close, contrary to common belief, the National Institute on Drug Abuse reports that marijuana can be addictive. Research suggests that about 1 in 11 users becomes addicted to marijuana (Anthony, 1994; Lopez-Quintero 2011). This number increases among those who start as teens (to about 17 percent, or 1 in 6) (Anthony, 2006) and among people who use marijuana daily (to 25-50 percent) (Hall & Pacula, 2003).
(Anthony J, Warner LA, Kessler RC. Comparative epidemiology of dependence on tobacco, alcohol, controlled substances, and inhalants: basic findings from the National Comorbidity Survey. Exp Clin Psychopharmacol. 1994;2:244-268.)
(Lopez-Quintero C, Pérez de los Cobos J, Hasin DS, et al. Probability and predictors of transition from first use to dependence on nicotine, alcohol, cannabis, and cocaine: results of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Drug Alcohol Depend. 2011;115(1-2):120-130.)
(Hall WD, Pacula RL. Cannabis Use and Dependence: Public Health and Public Policy. Cambridge, UK: Cambridge University Press; 2003.)
A significant area of concern? The amount of THC in marijuana has been increasing steadily over the past few decades. It is believed higher THC levels may mean a greater risk for addiction if users are regularly exposing themselves to high doses.