Marijuana impairs memory in long-term use, researchers warn

medical marijuana

Marijuana’s popularity continues to rise, both for medical and recreational uses but a new study finds that long-term use of cannabis and cannabis-based drugs impairs memory.

Researchers found that mice exposed to the drug long-term had “significant … memory impairments” and could not even discriminate between a familiar and novel object. The study has implications for both recreational users and for those who use the drug to combat epilepsy, multiple sclerosis and chronic pain. Earlier studies have found marijuana use disorders increasing substantially as usage grows.

Researchers from Lancaster and Lisbon Universities studied the effects of the cannabinoid drug WIN 55,212-2 in mice and found that:

  • Long-term exposure impairs learning and memory in the animals;
  • Brain imaging studies showed that the drug impairs function in key brain regions involved in learning and memory; and
  • Long-term exposure to the drug impairs the ability of brain regions involved in learning and memory to communicate with each other, suggesting that this underlies the negative effects of the drug on memory.

“Cannabis-based therapies can be very effective at treating the symptoms of chronic diseases such as epilepsy and multiple sclerosis, and dramatically increase the quality of life for people living with these conditions. We need to understand the side effects that these people may experience so that we can develop new interventions to minimize these side effects,” said Dr. Neil Dawson, the lead researcher from Lancaster University, in a news release.

“This work offers valuable new insight into the way in which long-term cannabinoid exposure negatively impacts on the brain. Understanding these mechanisms is central to understanding how long-term cannabinoid exposure increases the risk of developing mental health issues and memory problems,” he said.

“Could cause marked imbalances”

Professor Ana Sebastiao, lead researcher at the University of Lisbon, said the study, published in the Journal of Neurochemistry, “clearly shows that prolonged cannabinoid intake, when not used for medical reasons, does have a negative impact in brain function and memory.”

“It is important to understand that the same medicine may re-establish an equilibrium under certain diseased conditions, such as in epilepsy or MS, but could cause marked imbalances in healthy individuals,” she said. “As for all medicines, cannabinoid based therapies have not only beneficial disease-related actions, but also negative side effects. It is for the medical doctor to weight the advantages of the therapy, taking into consideration quality of life and diseases progression, against the potential side effects.”

A 2015 study conducted by Columbia University and published in JAMA Psychiatryfound that nearly three out of ten marijuana users experienced a marijuana use disorder of abuse or dependence in 2012-13, affecting some 6,846,000 Americans.

“At a time when Americans increasingly view marijuana use as harmless and favor its legalization, our findings suggest the need for caution and more public education about the potential for harms is warranted,” said Deborah Hasin, PhD, professor of clinical epidemiology at Columbia University’s Mailman School of Public Health. “This information is important to convey in a balanced manner to health professionals, policy makers and the public as the U.S. continues to consider legalization.”

Hasin’s study found that marijuana use in the United States more than doubled over the period from 2001-2002 to 2012-2013, while the increase in disorders associated with marijuana use was almost as large for that time period.

These findings were generally consistent across age, sex, race/ethnicity, education, income, urban/rural and region of the U.S. The results were also consistent with other studies showing increases in problems associated with cannabis, for example, cannabis-related emergency room visits and fatal car crashes, and indicate that as the prevalence of U.S. marijuana users increases, so will the number of individuals at risk for cannabis-related problems.

On a brighter note, a later study by Hasin found that legalizing medical marijuana has not increased recreational use of the substance among U.S. adolescents, according to a 2018 study published online in the journal Addiction.

 “For now, there appears to be no basis for the argument that legalizing medical marijuana has increased teens’ use of the drug,” said Hasin in a news release. “However, we may find that the situation changes as commercialized markets for medical marijuana develop and expand, and as states legalize recreational marijuana use.”

 

 

About the Author

Truman Lewis
Truman has been a bureau chief and correspondent in D.C., Los Angeles, Phoenix and elsewhere, reporting for radio, television, print and news services, for more than 30 years. Most recently, he has reported extensively on health and consumer issues for ConsumerAffairs.com and FairfaxNews.com.