Cannabis and memory

The long-term effects of cannabis have been the subject of ongoing debate. Because cannabis is illegal in most countries, research presents a challenge; as such, there remains much to be concluded.

There is evidence that cannabis use during adolescence, at a time when the brain is still developing, may have deleterious effects on neural development and later cognitive functioning. Rat models using synthetic cannabinoids have been criticized, as they are not necessarily translatable to human exposures. Acute cannabis intoxication has been shown to affect alterations in attention, psychomotor task ability, and short-term memory; however, a dose-response relationship has not been formally established through blind, randomized placebo controlled trials. While structural changes have been shown, studies have not demonstrated causation between cannabinoids and functionally significant long-term central nervous system effects of the drug or negative changes to brain composition.

Misrepresentation of data as demonstrating significance particularly regarding cannabinoids is a rampant issue in the scientific community and many of the studies that demonstrate structural changes in the brain have deluded confounding variables and selection bias that renders much of their data useless in drawing meaningful conclusions. Acute intoxication effects are often misrepresented as long term cognitive effects. Data has demonstrated, though, that chronic cannabis exposure needs longer to "wash out" of users and thus the acute intoxication effects appear to persist. Adequate time for wearing off produces data that demonstrates no difference in the performance of cognitive tasks.

Cannabis is the most widely used illicit drug in the Western world, and in the US 10 to 20% of consumers who use cannabis daily become dependent. Cannabis use disorder is defined in the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) as a condition requiring treatment. A 2012 review of cannabis use and dependency in the US by Danovitch et al said that in the US, "42% of persons over age 12 have used cannabis at least once in their lifetime, 11.5% have used within the past year, and 1.8% have met diagnostic criteria for cannabis abuse or dependence within the past year. Among individuals who have ever used cannabis, conditional dependence (the proportion who go on to develop dependence) is 9%." Although no medication is known to be effective in combating dependency, combinations of psychotherapy such as cognitive behavioural therapy and motivational enhancement therapy have achieved some success.

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