Persistent cannabis users show neuropsychological decline from childhood to midlife

Abstract

Recent reports show that fewer adolescents believe that regular cannabis use is harmful to health. Concomitantly, adolescents are initiating cannabis use at younger ages, and more adolescents are using cannabis on a daily basis. The purpose of the present study was to test the association between persistent cannabis use and neuropsychological decline and determine whether decline is concentrated among adolescent-onset cannabis users. Participants were members of the Dunedin Study, a prospective study of a birth cohort of 1,037 individuals followed from birth (1972/1973) to age 38 y. Cannabis use was ascertained in interviews at ages 18, 21, 26, 32, and 38 y. Neuropsychological testing was conducted at age 13 y, before initiation of cannabis use, and again at age 38 y, after a pattern of persistent cannabis use had developed. Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents.annabis, the most widely used illicit drug in the world, is increasingly being recognized for both its toxic and its therapeutic properties (1). Research on the harmful and beneficial effects of cannabis use is important because it can inform decisions regarding the medicinal use and legalization of cannabis, and the results of these decisions will have major public-health consequences. As debate surrounding these issues continues in the United States and abroad, new findings concerning the harmful effects of cannabis on neuropsychological functioning are emerging.Accumulating evidence suggests that long-term, heavy cannabis use may cause enduring neuropsychological impairmentimpairment that persists beyond the period of acute intoxication (2). Studies of long-term, heavy cannabis users fairly consistently show that these individuals perform worse on neuropsychological tests (2-5), and some (6-8) but not all (9) studies suggest that impairment may remain even after extended periods of abstinence. The magnitude and persistence of impairment may depend on factors such as the quantity, frequency, duration, and age-of-onset of cannabis use (2), as more severe and enduring impairment is evident among individuals with more frequent and prolonged heavy use and a younger age-of-onset (3,6,8,(10)(11)(12)(13)(14)(15)(16).The extant evidence base draws on case-control studies of recruited cannabis users and comparison subjects. These studies screen participants for potential confounding factors, such as alcohol and drug dependence, and compare them...

Cannabis users have higher premorbid IQ than other patients with first onset psychosis

“…None of these variables were found to have a significant association with either IQ or premorbid IQ among cases or controls (all p N .05). We only found that controls who had smoked cannabis after age 16, had higher IQ than controls that had smoked cannabis earlier in life (p = .016) (see also Meier et al, 2012) (Table 3). There was also a significant main effect of cannabis use (F(1,222) = 8.1, p = .005, η 2 = 0.036).…”

“…This is unexpected as it has been shown that cannabis use can impair cognition in healthy subjects (Fried et al, 2005;Meier et al, 2012).…”

Adolescent Cannabinoid Exposure Permanently Suppresses Cortical Oscillations in Adult Mice

“…Long-term cognitive impairments and elevated risk of psychiatric disorders in regular marijuana users are less pronounced when use is initiated in adulthood, instead of in adolescence (Arsenault et al, 2004;Meier et al, 2012). Our hypothesis predicts that the long-term effects of WIN on cortical oscillations would be restricted to adolescent exposure.…”

“…Persistent marijuana use before adulthood may permanently impair cognitive functioning (Solowij et al, 2002;Meier et al, 2012) and confer a higher risk of developing psychiatric diseases, such as schizophrenia, in susceptible individuals (Arseneault et al, 2004). Chronic adolescent, but not adult, cannabinoid exposure produces lasting working memory impairments and recapitulates other schizophrenia endophenotypes in rodents, including impaired sensorimotor gating, social avoidance, and anhedonia/avolition (Schneider and Koch, 2003;O'Shea et al, 2004;Quinn et al, 2008).…”

Medical Marijuana and Driving: a Review

“…Smoked marijuana may also adversely affect pulmonary function and immune modulation, leading to increased risk of pulmonary infections [10]. Chronic use of cannabis may be associated with persistent cognitive delays [11]. Long-term cannabis use is thought to produce irreversible impairment in memory, attention, and the organization and integration of complex functions [12].…”