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education, gender, gender × group and gender × wave, there were no significant
between-group differences and only CVLT immediate recall reached adjusted
statistically significant longitudinal change associated with changed cannabis use
(group × wave P 0.007). Specifically, former heavy users improved their performance
relative to remaining heavy users (estimated marginal means: former heavy 6.1-7.5:
remain heavy 6.4-6.6).
CONCLUSIONS: Cessation of cannabis use appears to be associated with an
improvement in capacity for recall of information that has just been learned. No
other measures of cognitive performance were related to cannabis after controlling
for confounds.
— Cannabis use and cognitive function: 8-year trajectory in a young adult
cohort (Tait, 2011) [49]
En metastudie från 2011 kommer till slutsatsen att det möjligen finns kvarvarande nedsättningar på
kognitiva funktioner hos kroniska cannabisrökare, bl.a kopplat till talförmågan, men att flertalet andra
påvisade nedsättningar har försvunnit efter abstinensfasen:
“
The trajectory of effects of cannabis on executive functions follows an interesting
pattern of recovery of some functions and persisting deficits in others (Table 2). The
acute effects of cannabis use are evident in attentional and information processing
abilities with recovery of these functions likely after a month or more of abstinence.
Decision-making and risk taking problems are not necessarily evident immediately
after smoking; however, if cannabis use is heavy and chronic, impairments may
emerge that do not remit with abstinence, particularly if heavy use was initiated in
adolescence, such that maturation of executive functions was not achieved. Acute
cannabis use impairs inhibition and promotes impulsivity, and over a period of
abstinence, these deficits are most evident in tasks that require concept formation,
planning, and sequencing abilities. Working memory is significantly impaired after
acute exposure to cannabis; however, these deficits resolve with sustained
abstinence. Evidence is less clear in regards to verbal fluency abilities; however,
research suggests that chronic, heavy use may impact verbal fluency abilities even
after long-term abstinence. The long-term effects of cannabis on executive function is
most clearly demonstrated when studies use chronic, heavy cannabis users, as
opposed to light, occasional users. Yet even occasional cannabis use can acutely
impair attention, concentration, decision-making, inhibition, impulsivity, and
working memory.
— Evidence-Based Review of Acute and Long-Term Effects of Cannabis Use on
Executive Cognitive Functions (Crean 2011) [33]
”
En studie från 2012 (presenterad 2010) visar att en tidig debut ger en större negativ effekt [50] :
Researchers at Harvard-affiliated McLean Hospital have shown that those who start
using marijuana at a young age are more impaired on tests of cognitive function than
those who start smoking at a later age.
“
Staci A. Gruber reported that subjects who started using marijuana before age 16
made twice as many mistakes on tests of executive function, which includes planning,
flexibility, abstract thinking, and inhibiting inappropriate responses, as those who
began smoking after age 16.
...
The study included 33 chronic marijuana smokers and 26 control subjects who did
not smoke marijuana. They were given a battery of neurocognitive tests assessing
executive function, including the Wisconsin Card Sorting Test, which involves sorting
different cards based on a set of rules given. During the test, the rules are changed
without warning and subjects must adjust their responses to the new rules.
”
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