"Street" Marijuana Harmful to
Cognitive Function in MS Patients
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Medical Update Memo
February 28, 2008
SUMMARY
Researchers have found that, in a small sample
of people with MS who admitted smoking marijuana
(Cannabis) regularly, measures of cognitive
function indicate some impairment. This study
does not address the question of whether
smoking marijuana causes long-term cognitive
impairment after use of the drug is discontinued.
Omar Ghaffar, MD, FRCP(C) and Anthony Feinstein
MPhil, PhD, FRCP(C) (Sunnybrook Health Services
Centre, Toronto Canada) report their findings
in the February 13 early online edition of
the journal Neurology. This study adds to
the growing body of literature on marijuana
in MS. The National MS Society will soon
publish an expert opinion paper on this subject
that was written by a task force appointed
to study the status of this ongoing area
of MS research.
DETAILS
Some people with MS report that smoking marijuana
relieves several of their MS symptoms, such
as spasticity and pain. However, scientific
studies completed thus far have not generally
provided convincing evidence that marijuana
or its derivatives provide substantiated
benefits for symptoms of MS.
Cognitive impairment is a troublesome symptom
experienced by a significant portion of people
with MS. This study asks important questions
about whether use of marijuana by people with
MS increases the risk of cognitive impairment.
In this study, Drs. Ghaffar and Feinstein evaluated
140 consecutive patients with MS using a standardized
psychiatric diagnostic interview and a battery
of neuropsychological tests. Among this group,
95 people said that they had never used illicit
drugs; 32 admitted that they had used cannabis
at least once; and 10 were classified as being
current users who smoked marijuana frequently
(daily, weekly, or monthly) and had used it
last from one to 30 days before the interviews.
Psychiatric and cognitive test results for
each of these 10 patients were compared with
four matched controls from the group who had
never used marijuana, 40 in all.
In that comparison, the proportion of patients
meeting the criteria for any psychiatric diagnosis
was higher in the 10 cannabis users than in
the matched non-users. Also, users had a slower
performance time on a test of information processing
speed, working memory, and sustained attention.
Although this study suggests that smoking marijuana
is associated with impaired cognition in people
with MS, further study is necessary to determine
if using cannabis causes the impairment. The
authors note some limitations of the study,
such as the small sample size and the fact
that marijuana use was assessed via patient
report and not by urine toxicology testing.
Also, marijuana is known to cause short-term
memory and other cognitive impairments in users
in the general population, but studies of how
permanent such impairment is once a person
stops using the drug have had mixed results,
some suggesting no lasting impairment and some
suggesting some residual cognitive impairment.
This study was not designed to evaluate that
question in users who have MS.
For more information on this topic as well
as a video clip of Dr. Feinstein discussing
trial results, click on the link below.
www.sunnybrook.ca/news?id=514
[With information from the National MS Society
(USA)]
ASK MS Information System Code: 1.4.1.20.i2
Disponible en français.
Disclaimer
The Multiple Sclerosis Society of Canada is an independent, voluntary health
agency and does not approve, endorse or recommend any specific product or
therapy, but provides information to assist individuals in making their own
decisions.
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