How Long-Term Marijuana Use Affects Memory

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People have been using marijuana (aka cannabis) for its psychoactive, spiritual, and medicinal purposes as far back as 2500 BC. Nevertheless, research on the side effects of marijuana remains limited because of its illegal status in the U.S. and many other countries. Although the results of existing studies are mixed, some research suggests that the long-term effects of marijuana use might include issues with memory, speed of thought, and other cognitive abilities.

Causes

The nervous system relies on an important communication network formed by neurons in the brain, called the endocannabinoid system. The active compound in cannabis, tetrahydrocannabinol (THC), attaches to and activates cannabinoid receptors on these neurons, disrupting its normal function. so its effects are profound.

Research Overview

Marijuana's negative effects on short-term memory are well-documented. However, when it comes to long-term memory, the effects of cannabis are not as clear or consistent. Ongoing research into cannabis' effects on memory in long-term users yields results that sometimes conflict, and recent research has begun to uncover some positive effects, too.

Cognitive Effects

As research on marijuana's effects on the brain expands, so too do their conclusions. For example:

  • In 2006, researchers studying heavy marijuana users (defined as four or more joints per week) found that they performed worse than non-users on a test of cognitive abilities. Those who had smoked for more than 10 years had more problems with their thinking abilities than those who had used for five to 10 years.
  • A 2021 research review leaned toward impairment of long-term memory among people who use cannabis heavily.
  • Conversely, in a 2021 study, participants who used cannabis at least once a month for at least two years evidenced no negative effects on long-term memory.

Notably, recent studies even indicate that the negative effects of marijuana on cognitive functions such as long-term memory can be reversed with abstinence from the drug.

Benefits

Increasingly, research is uncovering evidence that cannabis actually can improve brain health. Just a small sampling:

  • A 2019 study mostly in animals hinted at marijuana's potential to slow or prevent the advance of neurodegenerative illnesses that degrade memory, such as Huntington's disease, Alzheimer’s disease, and epilepsy.

  • A 2017 study showed that chronic low doses of THC restored cognitive function in old mice.

CBD

Cannabidiol (CBD), a nonpsychoactive component of marijuana that entered mainstream use in the last decade, offers a slew of documented benefits. Among these is its ability to help ease the symptoms of psychosis, anxiety, and behaviors associated with depression. It has even been shown to help those with post-traumatic stress disorder (PTSD) forget "painful and intrusive memories."

CBD shows no evidence that it negatively affects cognitive function. In fact, it may help counter memory problems and stave off brain diseases that affect memory, such as dementia, Alzheimer's disease, and Parkinson’s disease.

Frequently Asked Questions

  • Does marijuana have a long-term effect on the brain?

    Research on marijuana is as yet relatively limited, but it does suggest that chronic cannabis use negatively affects cognition. This is particularly true among people who begin consuming marijuana in adolescence.

  • What is considered heavy marijuana use?

    For research purposes, heavy cannabis use is typically defined as around two to three times per week.

  • Does marijuana kill brain cells?

    Researchers differ on whether cannabis kills brain cells, but many recent studies indicate that, no, it does not. However, it can cause other effects in the brain, such as impaired cognition. These effects may be reversible with abstinence.

12 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Donahue, M.  Earliest evidence for cannabis smoking discovered in ancient tombsNatl Geogr Mag. 2019.

  2. National Academies of Sciences. Challenges and Barriers in Conducting Cannabis Research. National Academies Press (US); 2017.

  3. National Institute on Drug Abuse. How does marijuana produce its effects?

  4. Messinis L, Kyprianidou A, Malefaki S, Papathanasopoulos P. Neuropsychological deficits in long-term frequent cannabis usersNeurology. 2006;66(5):737-739. doi:10.1212/01.wnl.0000201279.83203.c6

  5. The short-term and long-term effects of cannabis on cognition: Recent advances in the fieldCurrent Opinion in Psychology. 2021;38:49-55. doi:10.1016/j.copsyc.2020.07.005

  6. Binkowska AA, Jakubowska N, Gaca M, Galant N, Piotrowska-Cyplik A, Brzezicka A. Not just a pot: Visual episodic memory in cannabis users and polydrug cannabis users: ROC and ERP preliminary investigationFront Hum Neurosci. 2021;0. doi:10.3389/fnhum.2021.677793

  7. Yücel M, Lorenzetti V, Suo C, et al. Hippocampal harms, protection and recovery following regular cannabis useTransl Psychiatry. 2016;6(1):e710-e710. doi:10.1038/tp.2015.201

  8. Kim SH, Yang JW, Kim KH, Kim JU, Yook and TH. A review on studies of marijuana for alzheimer’s disease – focusing on CBD, THC. 2019;22(4):225-230. doi:10.3831/KPI.2019.22.030

  9. Silvestro S, Mammana S, Cavalli E, Bramanti P, Mazzon E. Use of cannabidiol in the treatment of epilepsy: Efficacy and security in clinical trialsMolecules. 2019;24(8):1459. doi:10.3390/molecules24081459

  10. Bilkei-Gorzo A, Albayram O, Draffehn A, et al. A chronic low dose of Δ9-tetrahydrocannabinol (THC) restores cognitive function in old miceNat Med. 2017;23(6):782-787. doi:10.1038/nm.4311

  11. Maroon J, Bost J. Review of the neurological benefits of phytocannabinoids. Surg Neurol Int. 2018;9:91. doi:10.4103/sni.sni_45_18

  12. Curran T, Devillez H, YorkWilliams SL, Bidwell LC. Acute effects of naturalistic THC vs. CBD use on recognition memory: A preliminary studyJournal of Cannabis Research. 2020;2(1):28. doi:10.1186/s42238-020-00034-0

Additional Reading

By Buddy T
Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.