Long-term marijuana use may fog the brain
Long-term users of marijuana gradually become worse at learning and remembering things, a new study suggests.
http://www.newscientist.com/article/dn8839-longterm-marijuana-use-may-fog-the-brain.html
There is some evidence from human studies that long-term marijuana use
can have adverse effects, although it seems that the spectrum of these
effects is narrower than previously thought and mainly centres around
cognitive (intellectual) function.
A paper in the Journal of the American Medical Association (JAMA) vol.
287 No. 9, March 6, 2002, pp. 1123-1131) found that long-term cannabis
users performed less well than shorter-term users and controls (people
who didn’t use cannabis) in tests of memory and attention. The
long-term users averaged 23.9 years of use, compared with 10.2 years
in the shorter-term users. You can find an abstract at the American
Medical Association web site:
http://jama.ama-assn.org/issues/v287n9/abs/joc11416.html , but access
to the full text requires subscription to the journal. Note that the
comments associated with the article (links to them are underneath the
abstract) indicate that some other investigators do not agree with
this conclusion.
Another study published in a Canadian medical journal (CMAJ 2002 Apr
2;166(7):887-91
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11949984&dopt=Abstract)
found that: “Current marijuana use had a negative effect on global IQ
score only in subjects who smoked 5 or more joints per week. A
negative effect was not observed among subjects who had previously
been heavy users but were no longer using the substance. We conclude
that marijuana does not have a long-term negative impact on global
intelligence.” This study compared IQ scores of individuals aged 9-12
years before they started using cannabis, with their scores at 17-20
years. Light users, former users and non-users showed a gain in IQ
over the same period.
One reason for the decreased IQ and memory in consistent heavy users
could be the fact that long-term cannabis use has been found to
decrease blood flow to the front areas of the brain (Neurotoxicology
and Teratology 2001 Sep-Oct; vol 23 pp. 437-43 Frontal lobe
dysfunction in long-term cannabis users by Lundqvist T, Jonsson S,
Warkentin S. of the Division of Medical Neurochemistry, Lund
University Hospital, 221 85, Lund, Sweden
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11711246&dopt=Abstract
A study published in Public Health and Nutrition, June 2001, vol. 4
pp. 781-786 (Dietary intake and nutritional status of US adult
marijuana users: results from the Third National Health and Nutrition
Examination Survey. By Smit E, Crespo CJ. of the Department of Social
and Preventive Medicine, SUNY School of Medicine, University at
Buffalo, Buffalo, NY 14214, USA.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11415485&dopt=Abstract
) found that marijuana users have lower levels of carotenoids in the
serum. The authors concluded this was associated with different
dietary habits: “We found higher cigarette-smoking rates and higher
consumption of sodas and alcohol, specifically beer, among marijuana
users than among non-current marijuana users. Marijuana users also
consumed more sodium, fewer fruits, and more pork, cheese, and salty
snacks.” Carotenoids are important anti-oxidants which help to
prevent cancer and other diseases. An increased risk of these
diseases might be due not so much to marijuana use itself as to the
lifestyle led by many who use it. Better attention to nutrition, in
order to ensure a good intake of fresh fruit and vegetables,
particularly the red, yellow and orange ones, will help to boost
antioxidant status (see below)
A review of various studies came to the conclusion that: “Regular
marijuana use can lead to extensive airway injury and alterations in
the structure and function of alveolar macrophages, potentially
predisposing to pulmonary infection and respiratory cancer.” Alveolar
macrophages are cells in the lungs that help clear away debris and
bacteria. (Current Opinions in Pulmonary Medicine, March 2001, vol 7
pp 43-61, Airway effects of marijuana, cocaine, and other inhaled
illicit agents. by Tashkin DP of the Division of Pulmonary and
Critical Care Medicine, UCLA School of Medicine, Los Angeles,
California 90095-1690
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11224724&dopt=Abstract
) Again, to counteract these effects, a diet high in antioxidants
would be helpful.
Obviously, marijuana smoked as joints and mixed with tobacco could
carry all the health risks associated with cigarette smoking. The use
of marijuana alone might be implicated in cancer. However, one review
concluded that: “While there is no doubt that marijuana smoke contains
carcinogens, an increase in cancer among users has thus far been
anecdotal. Because of the long latent period between cancer induction
and initiation of cigarette smoking, the full story is yet to be
told.” (International Journal of Neuropsychopharmacology, July 1998,
vol. 1 pp 71-80, Health aspects of cannabis: revisited. by Hollister
LE. of Harris County Psychiatric Center, University of Texas-Houston,
Houston, TX
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11281947&dopt=Abstract
) In support of this statement, I only found one recent paper in
Medline describing a case of cancer in one marijuana user. This in
itself is not absolute proof.
L E Hollister also concluded that: “Many older concerns about adverse
effects on health (chromosomal damage, 'cannabinol psychosis',
endocrine abnormalities, cardiac events, impaired immunity) no longer
seem to elicit much interest. Continuing concerns about the adverse
cognitive effects of chronic use indicate that these can be
demonstrated by proper testing; some studies suggest that they may be
long-lasting. Although cannabis does not produce a specific psychosis,
the possibility exists that it may exacerbate schizophrenia in persons
predisposed to that disorder.” i.e. the effects tend to be more on
brain function than on other diseases, and it could worsen the status
of people who have a tendency to schizophrenia.
