We’ve all internalized the stereotype of the lazy, forgetful stoner gorging on junk food while watching cartoons, but how much of this image is real, and how much is anti-cannabis propaganda? Does weed make you forgetful? Our scientific review investigates the impact of cannabis on memory.
Does Weed Make You Forgetful?
As with many stereotypes, the forgetful “burned out” stoner image contains a kernel of truth. It’s clear from the research that people who use marijuana have significantly worse memory while they are high, but long-term memory effects of heavy use are more of a subject of controversy in the world of medical research than in popular imagination.
In fact, some preliminary research and anecdotal evidence shows cannabis can actually have a protective effect on memory in people who suffer age-related dementia, brain trauma-related dementia and Alzheimer’s.
Research continues in earnest on the cognitive and memory declines associated with heavy cannabis use. But the most recent and comprehensive look at this issue shows that cannabis use by adults can cause minor, temporary memory impairments which go away shortly after these adults quit using cannabis. These results held even when the subjects were adolescents and young adults whose brains were still developing.
“Although continued cannabis use may be associated with small reductions in cognitive functioning, results suggest that cognitive deficits are substantially diminished with abstinence,” according to a 2018 study published in the Journal of the American Medical Association’s psychiatry journal. “Participants showed a small but significant overall effect size for reduced cognitive functioning in adolescents and young adults who reported frequent cannabis use. However, studies requiring abstinence from cannabis for longer than 72 hours had a very small, non-significant effect size.”
Some studies show that long-term daily use in adults can cause memory problems linked to the main psychoactive chemical in marijuana, Delta-9 tetrahydrocannabinol (THC). Test subjects tend to perform more poorly on standardized memory tests, appearing more forgetful, for up to six weeks after cessation of marijuana use.
Be sure to read our article on Marijuana Induced Memory Loss And How To Combat It. It contains a ton of insights to minimize the effects of cannabis on memory, specifically the forgetful side effects.
“Relatively consistent findings have been reported regarding the acute impairments induced by a single dose of THC on verbal and working memory,” states a 2013 study in the journal Substance Abuse Rehabilitation. “It is unclear whether they may persist beyond the intoxication state. In the long-term, these impairments seem particularly likely to manifest and may also persist following abstinence if regular and heavy use of cannabis strains high in THC is started at an early age.”
But as with many studies of marijuana use, the fact it’s still illegal on a federal level in the U.S. and in many other countries makes it difficult to measure objectively. Often, studies focus on self-reporting and contain no control groups or accurate dosage information, or even information on the cannabis strain type and quality. All these missing variables can render study results virtually useless.
“Future experimental and epidemiological studies that take into consideration individual differences, particularly previous cannabis history and demographic characteristics, but also the precise mixture of the ingredients of the consumed cannabis are necessary to clarify the magnitude (of) cannabis-induced memory impairments,” according to the 2013 study mentioned above.
One example of study problems? The tendency of heavy recreational cannabis users to use other drugs as well. Cannabis use disorder is outlined in the psychological diagnostic Bible, the DSM-V. Daily pot smokers tend to meet the criteria for this disorder, but in one study, 82 percent of the participants also met criteria for alcohol use disorder and 48 percent were addicted to tobacco as well.
“Thus, among typical marijuana users, it is difficult to disentangle the neural effects of marijuana from those associated with other substances,” states a 2008 study in Current Drug Abuse Review.
Does Cannabis Use as a Teenager Harm Your Brain?
One thing does seem clear about cannabis use and memory impairment: teenagers who are heavy weed users are much more vulnerable to potential long-term memory problems from marijuana use. Adolescence is a time of extensive brain growth and development, and introducing substances like marijuana — or alcohol and other drugs — has an outsized effect when compared with similar use patterns by adults.
In fact, prolonged cannabis use has even been shown to decrease the size of your hippocampus, your brain region responsible for encoding new memories.
“When people begin using marijuana as teenagers, the drug may impair thinking, memory, and learning functions and affect how the brain builds connections between the areas necessary for these functions,” according to the NIDA. “Researchers are still studying how long marijuana’s effects last and whether some changes may be permanent.”
Even this assumption about early pot smoking is far from established fact, though.
A New Zealand study showed an average drop of 6 IQ points among heavy weed users from age 13 to 38. That cognitive function didn’t seem to return for these subjects after they quit smoking as adults. Conversely, the same study showed little to no cognitive decline among participants who started smoking pot as adults.
But another study published recently and focusing on twins contradicted the New Zealand results. Subjects measured at ages 9 to 12 who then used marijuana heavily during adolescence showed a drop of about 4 IQ points by the time they were 17-18, but those who ended up being heavy users had lower scores in the first place.
Be sure to read our related article: Does Smoking Weed As a Kid Make You Dumb?
More importantly, there was no difference between twins who used cannabis in their teen years and their siblings who did not.
“This suggests that the IQ decline in marijuana users may be caused by something other than marijuana, such as shared familial factors (e.g., genetics, family environment),” according to NIDA.
How does the trend toward stronger weed affect memory?
One factor that worries memory impairment researchers looking at cannabis is the trend toward wider use in the population of ever-stronger strains and distillates of cannabis.
“The amount of THC in marijuana has been increasing steadily over the past few decades,” according to NIDA. “For a person who’s new to marijuana use, this may mean exposure to higher THC levels with a greater chance of a harmful reaction.”
The institute is currently undertaking a large long-term study on adolescent brain development to attempt to answer exactly how much cannabis use affects memory, makes you forgetful, and impacts brain development.
The Longitudinal Study of Adolescent Brain and Cognitive Development recruited 11,900 healthy kids and includes neuroimaging to help tease apart how environmental, social and biological factors affect their development over time. Ideally, this wide-ranging study will provide more solid conclusion about the cognitive effect of marijuana use among teens.
Until then…complimenting high-THC cannabis use with the other main cannabinoids in cannabis, cannabidiol (CBD), can help alleviate some of the negative side effects of chronic marijuana consumption. Other supplements and exercise can also help with the forgetful side-effects of marijuana.