A 15-year John Hopkins study on the long-term effects of marijuana use on mental function found negligible effects. These results have been
ignored by the mainstream press. Results of the study were published in the May 1, 1999 issue of the American
Journal of Epidemiology shown below.
From
Cannabis Use and Cognitive Decline in Persons under 65 Years of Age.
Constantine G. Lyketsos, Elizabeth Garrett, Kung-Yee Liang, and James C. Anthony
( Osler 320, The Johns Hopkins Hospital, 600 North Wolfe Street, Baltimore, MD
21287-5371)
Am J Epidemiol 1999;149:794-800
The purpose of this study was to investigate possible adverse effects of
cannabis use on cognitive decline after 12 years in persons under age 65 years.
This was a follow-up study of a probability sample of the adult household
residents of East Baltimore. The analyses included 1,318 participants in the
Baltimore, Maryland, portion of the Epidemiologic Catchment Area study who
completed the Mini-Mental State (MMSE) examination during three study waves in
1981, 1982, and 1993--1996. Individual MMSE score differences between waves 2
and 3 were calculated for each study participant. After 12 years, study
participants' scores declined a mean of 1.20 points on the MMSE (standard
deviation 1.90), with 66% having scores that declined by at least one point.
Significant numbers of scores declined by three points or more (15% of
participants in the 18--29 age group). There were no significant differences in
cognitive decline between heavy users, light users, and nonusers of cannabis.
There were also no male-female differences in cognitive decline in relation to
cannabis use. The authors conclude that over long time periods, in persons under
age 65 years, cognitive decline occurs in all age groups. This decline is
closely associated with aging and educational level but does not appear to be
associated with cannabis use.