PNAS：青春期开始使用大麻的人与智商衰退有关

一项研究提示，特别是在青春期开始使用大麻的人群当中，持续使用大麻可能与神经心理的衰退有联系。Madeline H. Meier及其同事对1972年到1973年间出生于新西兰但尼丁（Dunedin）的1037人的群体中的持续使用大麻情况和神经心理功能的联系进行了研究，并且对他们随访到了38岁。这组科研人员发现，报告了持续使用大麻的研究对象表现出了比其他受试者更大的智商衰退。持续使用大麻与5类神经心理功能的广泛削弱有联系，而且甚至在控制了教育年限以及使用包括酒精在内的其他毒品等变量之后仍然具有显著意义。根据受试者称之为“熟悉”的人的信息，持续使用大麻看上去影响了日常认知功能，持续使用大麻的人表现出了比其他受试者显著更多的注意力和记忆问题。在对持续的水平等效化之后，与成年期开始使用的人相比，青春期开始使用大麻的人倾向于变为更长期的使用者并且遇到更大的智商衰退。戒除或减少大麻的使用并不会全部恢复青春期开始使用大麻的人的神经心理功能，而这组作者推测说，青春期使用大麻——此时大脑正在进行关键的发育——可能产生神经毒素作用。这组作者说，这些发现表明应该对推迟大麻的首次使用投入更多的举措

Persistent cannabis users show neuropsychological decline from childhood to midlife

Madeline H. Meiera, Avshalom Caspi, Antony Amblere, HonaLee Harringtonb, Renate Houtsb, Richard S. E. Keefed, Kay McDonaldf, Aimee Wardf, Richie Poultonf, and Terrie E. Moffitt

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.