marijuana abstinence improves memory in teens

a small study in teenagers found that one week of cannabis abstention was associated with significant memory improvement (see marijuana abstinence improves memory jclinpsych2018 in dropbox, or doi-org.ezp-prod1.hul.harvard.edu/10.4088/JCP.17m11977)

Details:

-- 88 adolescents and young adults (age 16 to 25) who were regular cannabis users in 2015-16, from the community as well as a local high school

-- 55% male, mean age 21, 14 years of education, 64% white/15% black/3% Asian/9% Hispanic, psychiatric diagnoses: 4% major depression/4% PTSD/6% generalized anxiety disorder

-- baseline alcohol use in the past 90 days: 16 days of alcohol consumption, median number of drinks consumed 70

-- baseline cannabis use in past 90 days: 56 days of cannabis consumption, consumed 105 times, median consumption 26 g

-- People randomly assigned to 4 weeks of cannabis abstention, verified by decreasing urinary metabolites, vs a monitored control group with no abstinence requirement

-- attention and memory were assessed by the Cambridge Neuropsychological Test Automated Battery at baseline and weekly for 4 weeks

Results:

-- 55 (89%) in the intervention group had biochemically confirmed 30-day continuous abstinence; all in the control group continued to use

-- verbal memory improved in the 1^st week and continued (p= 0.002)

-- memory overall was better in those who were abstinent (review of the chart: those abstinent had major improvement in the first week, which remained the same for weeks 2-4; no change in memory in the control group)

-- declarative memory, and in particular encoding new information, was the aspect of memory most improved by marijuana abstention.

-- No significant effect was found specifically on visual span capacity, short-term visual recognition memory, and verbal recall of information after a delay

-- no effect of abstinence on attention: both improved equally, consistent with a practice effect

Commentary:

-- adolescent use of cannabis  is quite widespread: in 2016, 29% of middle and high school students had used marijuana, 23% at least annually, 14% in the past month, and 3% daily (rates of daily use doubling between 8^th and 12^th grades) [I did write up this National Survey last year, though it was inadvertently not published. Given its importance, I will publish it tomorrow.]

-- There are real concerns about cannabis exposure during adolescence and later neuromaturation, an effect which is likely to be particularly profound in adolescent marijuana users as their brains are developing

-- lots of previous studies have found an association between adolescent cannabis use and poor neurocognitive functioning. This current study suggests a few things:

    -- cannabis itself is associated with depressed cognitive functioning (not so surprising, but hard to prove by observational studies: eg, is it that people with somewhat depressed cognitive functioning smoke more marijuana?)

    -- Stopping cannabis for one month led to a rapid cognitive improvement, and this was evident in general in the 1^st week of abstinence and maintained itself for the rest of the study period. [is this an acute effect of cannabis on the brain, which reverses within 1 week? is there some underlying non-reversible component, suggesting that cannabis has really bad potential long-term cognitive effects/a new "normal"?]

-- The fact that marijuana interfered with new memory formation is consistent with the finding of a particularly high density of canabinoid type I receptors in the prefrontal cortex as well as in the frontal gray area [again, how much of this predated marijuana use or may even have led to marijuana use? and, is it reversible?]

-- a major limitation of the study was that there was no real control group of non-users. it would be great to have an RCT of teens never having used marijuana and then randomized to marijuana vs placebo, assessing the immediate and longer term cognitive effects.  but i suspect that this would not pass IRB muster....

So, the study does find that at least some important memory changes improve signficiantly even with short-term abstinence of one week, and even perhaps sooner than 1 week (not tested). the increase in marijuana use in teens is really striking, which is particluarly problematic for a few reasons:

--they are much more likely prone to long-term cognitive problems later (their brains are more plastic than in us older guys)

--the likelihood is that marijuana will become more widespread and available with loosening of laws/legalization

--it is pretty likely that many will buy cheaper marijuana on the streets (which is not regulated and pure), with the attendant risks of contamination with fentanyl, cocaine, etc (which we are now seeing)

--and, unfortunately, i'm not sure that we will ever know definitively the real short-term vs long-term effects of marijuana use.

but, it does make sense for us as clinicians to discourage marijuana use, given these potential longterm effects. the hard part is that there are many teens (including several whom i see) who do use marijuana several times a day, who  feel that using is the only way they can function in their high stress lives.  though i have had (i think) some success in decreasing the extent of the usage in some of them.

Older blogs on marijuana:

See http://gmodestmedblogs.blogspot.com/2014/06/marijuana-adverse-effects-review.html  for review of the short-term and long-term effects of marijuana (negative and positive)

See http://gmodestmedblogs.blogspot.com/2015/07/marijuana-passing-through-generations.html  for an interesting basic science article finding epigenetic changes in marijuana smoking rats, which seem to be inherited by the next generation (which, I think, blurs one of the fine lines of genetics/epigenetics: I had thought that epigenetics reflected largely environmental changes on the expression of aspects of the genetic code. If passed on to subsequent generations, acts more like genetics itself)

See http://gmodestmedblogs.blogspot.com/2014/03/marijuana-psych-effects.html  for some articles on the effects of marijuana on the adolescent rat brain, similar to some of the structural findings of schizophrenia; another article of a a meta-analysis of longitudinal studies finding a relationship between subsequent marijuana users and the development of psychosis

See http://gmodestmedblogs.blogspot.com/search?q=feel+good+gene for a review of an article suggesting that there was significant variation in genetics and susceptibility to using psychoactive drugs

geoff

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