The duration of marijuana use and cultivation in human history is remarkable. Records in China exist as far back as 6000 years ago, from the Neolithic age.1In Hindu scripture, cannabis is written in the Vedas, the fundamental religious texts of Hinduism, as one of the five sacred plants.2Today, it is estimated that there are over 180 million users of cannabis world-wide.3Given the increasing use and legalization of marijuana, it is imperative that the risks and benefits of the plant are well-understood.
Marijuana is composed of hundreds of compounds, but Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are the two most well-understood, and they are thought to mediate many of the psychological and physiological effects of marijuana use.4Interestingly, these compounds have different effects - THC increases anxiety and psychosis-like behavior while also reducing learning; CBD, on the other hand, has the exact opposite effects in humans.5Furthermore, THC and CBD have been shown to have opposing effects on brain activation during multiple emotional and cognitive tests. This evidence indicates CBD may reverse some of the harmful effects of THC, and for that reason, there is growing interest in investigating CBD for possible therapeutic benefits.
Population-wide studies linking marijuana to IQ and school performance changes are contentious. With regards to IQ, three large studies have been conducted in New Zealand, the US and the UK.6,7,8One study found a link between high cannabis use, particularly, in adolescence, and decreased IQ. Two studies did not find a significant effect of marijuana on IQ. However, the low levels of marijuana use in the cohorts used in those two negative studies led some to speculate that there was not enough cannabis use to elicit the IQ impairment observed in the study that showed IQ is reduced by cannabis use.
Regarding educational level achieved, several studies have consistently shown evidence of adolescent cannabis and worse educational outcomes. However, there is debate as to whether confounding factors have been taken into account, including socioeconomic and genetic factors.5
Another common perception of cannabis use is its improvement in creativity. However, the evidence is conflicting. In a study involving 60 participants, it was found that marijuana (THC) had no positive effects on and decreased divergent thinking in regular users when measured with the Torrance Tests of Creative Thinking.9In another investigation involving 54 participants, it was found that a low dosage (5.5 mg of THC) does not impact creativity while a high dosage (22 mg THC) impairs creativity when measured with a divergent thinking task.10Multiple studies have been conducted stratifying individuals with high and low scores on creativity tests, or dividing users based on expectations. Cannabis (THC) use was found to be associated with increased divergent thinking in individuals with low creativity.11Cannabis was also found to increase creative thinking in individuals normally with low creativity, based on the verbal fluency test.12After taking cannabis, their creativity level approaches similar levels to those individuals normally with high creativity. In another study of 566 participants, individuals exhibited improved performance in a divergent thinking task if they expected the use of marijuana to enhance creative problem solving.13
The use of marijuana for improving creativity is equivocal, and the impact of adolescent marijuana use on academic performance is not definitive. However, a great deal of basic research points to adverse effects on brain centers involved in regulating emotion and motivation. While these results have not borne out to human trials, there should be caution because of this evidence. There is also promising research around the use of CBD rather than THC, for reducing anxiety, and maintaining some of the positive benefits of marijuana, while avoiding the negative impact of THC. Much more research is needed around marijuana in general, but in particular around vulnerable populations, including adolescents and those with genetic predispositions to addiction.
Curran, H. V., Freeman, T. P., Mokrysz, C., Lewis, D. A., Morgan, C. J., & Parsons, L. H. (2016). Keep off the grass? Cannabis, cognition and addiction. Nat Rev Neurosci, 17(5), 293-306. doi:10.1038/nrn.2016.28
Meier, M. H., Caspi, A., Ambler, A., Harrington, H., Houts, R., Keefe, R. S., . . . Moffitt, T. E. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proc Natl Acad Sci U S A, 109(40), E2657-2664. doi:10.1073/pnas.1206820109
Mokrysz, C., Landy, R., Gage, S. H., Munafo, M. R., Roiser, J. P., & Curran, H. V. (2016). Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study. J Psychopharmacol, 30(2), 159-168. doi:10.1177/0269881115622241
Jackson, N. J., Isen, J. D., Khoddam, R., Irons, D., Tuvblad, C., Iacono, W. G., . . . Baker, L. A. (2016). Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies. Proc Natl Acad Sci U S A, 113(5), E500-508. doi:10.1073/pnas.1516648113
Kowal, M. A., Hazekamp, A., Colzato, L. S., van Steenbergen, H., van der Wee, N. J., Durieux, J., . . . Hommel, B. (2015). Cannabis and creativity: highly potent cannabis impairs divergent thinking in regular cannabis users. Psychopharmacology (Berl), 232(6), 1123-1134. doi:10.1007/s00213-014-3749-1
Minor, K. S., Firmin, R. L., Bonfils, K. A., Chun, C. A., Buckner, J. D., & Cohen, A. S. (2014). Predicting creativity: the role of psychometric schizotypy and cannabis use in divergent thinking. Psychiatry Res, 220(1-2), 205-210. doi:10.1016/j.psychres.2014.08.044
Schafer, G., Feilding, A., Morgan, C. J., Agathangelou, M., Freeman, T. P., & Valerie Curran, H. (2012). Investigating the interaction between schizotypy, divergent thinking and cannabis use. Conscious Cogn, 21(1), 292-298. doi:10.1016/j.concog.2011.11.009
Hicks, J. A., Pedersen, S. L., Friedman, R. S., & McCarthy, D. M. (2011). Expecting innovation: psychoactive drug primes and the generation of creative solutions. Exp Clin Psychopharmacol, 19(4), 314-320. doi:10.1037/a0022954
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