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Neuropsychological consequences of regular marijuana use: a twin study

Published online by Cambridge University Press:  21 October 2004

M. J. LYONS
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
J. L. BAR
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
M. S. PANIZZON
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
R. TOOMEY
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
S. EISEN
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
H. XIAN
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
M. T. TSUANG
Affiliation:
Department of Psychology, Boston University, Boston, MA, USA; Harvard Medical School, Department of Psychiatry at the Brockton/West Roxbury VA, USA; Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, MA, USA; Research and Medical Service, St. Louis VA, St. Louis, MO, USA; Division of General Medical Sciences, Department of Medicine, Washington University, St. Louis, MO, USA; Harvard Medical School, Department of Psychiatry at Massachusetts Mental Health Center, Boston, MA, USA; Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA

Abstract

Background. Results of previous research examining long-term residual effects of marijuana use on cognition are conflicting. A major methodological limitation of prior studies is the inability to determine whether differences between users and non-users are due to differences in genetic vulnerability preceding drug use or due to the effects of the drug.

Method. Fifty-four monozygotic male twin pairs, discordant for regular marijuana use in which neither twin used any other illicit drug regularly, were recruited from the Vietnam Era Twin Registry. A minimum of 1 year had passed since the marijuana-using twins had last used the drug, and a mean of almost 20 years had passed since the last time marijuana had been used regularly. Twins were administered a comprehensive neuropsychological test battery to assess general intelligence, executive functioning, attention, memory and motor skills. Differences in performance between marijuana-using twins and their non-using co-twins were compared using a multivariate analysis of specific cognitive domains and univariate analyses of individual test scores. Dose–response relationships were explored within the marijuana-using group.

Results. Marijuana-using twins significantly differed from their non-using co-twins on the general intelligence domain; however, within that domain only the performance of the block design subtest of the Wechsler Adult Intelligence Scale – Revised reached a level of statistical significance.

Conclusions. Out of the numerous measures that were administered, only one significant difference was noted between marijuana-using twins and their non-using co-twins on cognitive functioning. The results indicate an absence of marked long-term residual effects of marijuana use on cognitive abilities.

Type
Research Article
Copyright
© 2004 Cambridge University Press

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