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THREE THINGS MARIJUANA DOESN'T DO from California NORML Reports, April 1992
(1) NO BRAIN DAMAGE SEEN IN MARIJUANA-EXPOSED MONKEYS
Two new scientific studies have failed to find evidence
of brain damage in monkeys exposed to marijuana, undercutting
claims that marijuana causes brain damage in humans.
The studies were conducted by two independent
research groups. The first, conducted by Dr. William Slikker,
Jr. and others at the National Center for Toxicological Research
in Arkansas examined some 64 rhesus monkeys, half of which
were exposed to daily or weekly doses of marijuana smoke for
a year. The other, by Gordon T. Pryor and Charles Rebert at SRI
International in Menlo Park, California, which is still
unpublished, looked at over 30 rhesus monkeys that had inhaled
marijuana one to three times a day over periods of 6 to 12
months. Neither study found evidence of structural or
neurochemical changes in the brains of the monkeys when
examined a few months after cessation of smoking.
The new results cast doubt on earlier studies
purporting to show brain damage in animals. The most famous
of these was a study by Dr. Robert Heath, who claimed to find
brain damage in three monkeys heavily exposed to cannabis.
Heath's results failed to win general acceptance in the
scientific community because of the small number of subjects,
questionable controls, and heavy doses.
Subsequent rat experiments by Dr. Slikker and others
reported persistent structural changes in the brain cells of
rats chronically exposed to THC. The studies did not show that
pot kills brain cells, as alleged by some pot critics, but they
did show degeneration of the nerve connections between brain
cells in the hippocampus, where THC is known to be active.
Although scientists have regarded the animal evidence
as inconclusive, some critics have cited it as proof that pot
causes brain damage in humans. Thus Andrew Mecca, the
director of California Department of Alcohol and Drug Abuse,
recently stated on the Ron Reagan, Jr. talk show (Sep. 2, 1991)
that marijuana "leaves a black protein substance in the
synaptic cleft" of brain cells, a claim apparently based on
Heath's monkeys. When asked by a NORML member for his
evidence, Mecca sent a list of three references, none of which
turned out to have anything to do with brain damage.
Although the new monkey studies found no physical
brain damage, they did observe behavioral changes from
marijuana. Slikker's group found that monkeys exposed once a
day to the human equivalent of four or five joints showed
persistent effects throughout the day. Slikker says that the
effects faded gradually after they were taken off marijuana,
and were not detectable seven months later, when they were
sacrificed. Autopsies did reveal lingering chemical changes in
the immune cells in the lungs of monkeys that had inhaled THC.
However, Slikker's group concluded that experimental exposure
to marijuana smoke "does not compromise the general health of
the rhesus monkey."
References:
William Slikker, Jr. et al, "Chronic Marijuana Smoke Exposure in the Rhesus
Monkey," Fundamental and Applied Toxicology 17: 321-32 (1991)
Guy Cabral et al, "Chronic Marijuana Smoke Alters Alveolar Macrophage
Morphology and Protein Expression, Pharmacology Biochemistry and
Behavior 40: 643-9 (1991)
Merle Paule et al., "Chronic Marijuana Smoke Exposure in the Rhesus Monkey
II: Effects on Progressive Ratio and Conditioned Position
Responding," Journal of Pharmacology and Experimental Therapeutics
260: 210-22 (1992)
(2) POT FOUND NOT TO CAUSE FETAL ALCOHOL SYNDROME
A new study of children born to marijuana-smoking
mothers found no link between marijuana exposure and the
birth defects of fetal alcohol syndrome (FAS). The new study,
by Dr. Susan J. Astley of the University of Washington,
published in the January, 1992 issue of Pediatrics,
contradicted a 1982 study by Dr. Ralph Hingson, in which
prenatal exposure to marijuana was found to increase the risk
of FAS.
Hingson's results, which have not been replicated, have
been questioned on various methodological grounds, in
particular the difficulty of controlling for combined drinking
and pot use.
The new study looked for facial deformities
symptomatic of FAS in 40 children whose mothers had smoked
marijuana heavily during pregnancy and 40 controls, It found no
association between marijuana and FAS, but deformities were
observed in children of women who drank 2 ounces of alcohol
per day or took cocaine.
(3) NEW STUDY FINDS POT DOESN'T LOWER TESTOSTERONE
A new study by Dr. Robert Block at the University of
Iowa disputes the commonly held notion that marijuana alters
the level of testosterone and other sex hormones.
The study contradicted a widely publicized 1974 study
by Dr. R.C. Kolodony, which reported decreased testosterone
levels in men who smoked marijuana chronically.
The U. of Iowa study found that chronic marijuana use
had no effect on testosterone, luteinizing hormone, follicle
stimulating hormone, prolactin and cortisol in men or women.
Noting that six other studies had failed to show
lowered testosterone levels in men, Dr. Block concluded: "It
appears that marijuana, even heavy use of the kind that's
typical in the United States, doesn't alter testosterone levels."
However, he cautioned that heavy use might have other
adverse effects, including "possible effects on reproductive
function and mild, selective cognitive impairments associated
with heavy, chronic use."
Block's study is published in Drug and Alcohol
Dependence, Vol. 28: 121-8 (1991).