Early onset marijuana use is associated with learning inefficiencies.

Abstract

Objective Verbal memory difficulties are the most widely reported and persistent cognitive deficit associated with early-onset marijuana use. Yet, it is not known what memory stages are most impaired in those with early marijuana use. Method Forty-eight young adults, aged 18–25, who used marijuana at least once per week and 48 matched non-using controls (CON) completed the California Verbal Learning Test, Second Edition (CVLT-II). Marijuana users were stratified by age of initial use: ‘early onset’ users (EMJ), who started using marijuana at or before age 16 (n = 27), and ‘late onset’ marijuana user group (LMJ), who started using marijuana after age 16 (n = 21). Outcome variables included trial immediate recall, total learning, clustering strategies (semantic clustering, serial clustering, ratio of semantic to serial clustering, and total number of strategies used), delayed recall, and percent retention. Results Learning improved with repetition, with no group effect on the learning slope. EMJ learned fewer words overall than LMJ or CON. There was no difference between LMJ and CON in total number of words learned. Reduced overall learning mediated the effect on reduced delayed recall among EMJ, but not CON or LMJ. Learning improved with greater use of semantic versus serial encoding, but this did not vary between groups. EMJ was not related to delayed recall after adjusting for encoding. Conclusions Young adults reporting early onset marijuana use had learning weaknesses, which accounted for the association between early onset marijuana use and delayed recall. No amnestic effect of marijuana use was observed.

A Systematic Review of Human Neuroimaging Evidence of Memory-Related Functional Alterations Associated with Cannabis Use Complemented with Preclinical and Human Evidence of Memory Performance Alterations

“…We reviewed studies of both adults and adolescents, comparing the performance of memory tasks between CU to NU. Verbal memory performance was negatively affected by cannabis use [93,94,[96][97][98][102][103][104][105][106], with increased deficits associated with cannabis use levels [95,99,107]. This was also shown in a study of cannabis users ranging from light to heavy use after a month abstinence [132], in both adolescent and adult users, though deficits in performance were not reported in all studies [12,97,100,101].…”

“…Three studies used the California verbal learning test [101][102][103], with two finding that CU performed significantly worse than NU [102,103], and the third study no significant difference [101]. Levar et al only found a significant difference in the long-delay cued recall condition out of four tests of short and long delay free and cued recall with earlier-onset users performing worse than late-onset users [102], and Schuster et al found that CU performed significantly worse at encoding and recall only in early-onset users, i.e., before the age of 16 [103]. It is unclear whether duration of abstinence or extent of cannabis use may have accounted for the difference in results in these three studies.…”

“…Evidence from some studies suggests that longer duration of cannabis use may have an adverse impact on memory performance [93,107] with the amount of cannabis used correlating with performance in some studies [95,106], implying that high levels and longer use of cannabis are related to reduced memory performance. An increased likelihood of memory impairments was found to be associated with an earlier age of onset of cannabis use [103,133], although this association may also have been a result of the longer duration of exposure in those that started earlier and therefore the greater amount of cannabis that they had been exposed to and not necessarily an effect of earlier age of onset of use per se. This issue was investigated in one study that found significant deficits in early-onset users compared to late-onset users, despite late-onset users having used for longer periods [103], suggesting that there is very likely a developmentally sensitive period when the effects of cannabis exposure on memory performance are more prominent in humans, consistent with preclinical evidence [116,117,119,122].…”

The initiation of cannabis use in adolescence is predicted by sex‐specific psychosocial and neurobiological features

“…Cannabis use in adolescence is associated with a range of adversity in adulthood including cannabis dependence (DSM‐IV; Hall & Degenhardt, ; Moss, Chen, & Yi, ), poly‐drug use (Secades‐Villa, Garcia‐Rodríguez, Jin, Wang, & Blanco, ), cognitive deficits (Meier et al., ; Schuster, Hoeppner, Evins, & Gilman, ), compromised physical (Kalant, ) and mental health (Degenhardt et al., ; Kedzior & Laeber, ; Malone, Hill, & Rubino, ), and diminished life attainment goals (e.g., socioeconomic factors; Fergusson & Boden, ). These findings are supported by animal models linking adolescent cannabis exposure with detrimental outcomes in adulthood (O'Shea, ; Quinn et al., ).…”

Potencial uso terapéutico de cannabis

“…En un estudio reciente 31 , se evaluó el efecto del consumo de marihuana en 28 adultos jóvenes, los cuales fueron estratificados en consumidores tempranos y consumidores tardíos. En los individuos con consumo temprano se observó mayor lentitud en el aprendizaje de palabras, pero no se observaron efectos amnésicos.…”