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Cancer
Gibson et al, 1983; Hatch and Bracken, 1986; Zuckerman et al, 1989), and length at
birth (Tennes et al, 1985). This relationship has been found in the best controlled
studies, and it has persisted after statistically controlling for potential confounding
variables by sophisticated forms of statistical analysis (e.g. Hatch and Bracken, 1986;
Zuckerman et al, 1989).
Uncertainty remains about the interpretation of this finding. Is it because the
"marijuana products were toxic to foetal development", as argued by Nahas and
Latour (1992)? Is it because THC interferes with the hormonal control of pregnancy
shortening the gestation period, as has been reported by Gibson et al (1983) and
Zuckerman et al (1989)? The fact that the lower birth weight among the children of
women who used cannabis disappears after controlling for gestation length is
supportive of the latter hypothesis. Is it because cannabis is primarily smoked, since
tobacco smoking has been consistently shown to be associated with reduced birth
weight (Fried, 1993)?
The findings on the relationship between cannabis use and birth abnormalities are
more mixed, and conclusions accordingly less certain. Early case reports of children
with features akin to the Foetal Alcohol Syndrome born to women who had smoked
cannabis but not used alcohol during pregnancy (e.g. Milman, 1982, p42) suggested
that cannabis may increase the risk of birth defects. Subsequent controlled studies
have produced mixed results. Four studies have reported no increased rate of major
congenital abnormalities among children born to women who use cannabis (Gibson
et al, 1983; Hingson et al, 1982; Tennes et al, 1985; Zuckerman et al, 1989).
One study has reported a five-fold increased risk of children with foetal alcohol like
features being born to women who reported using cannabis (Hingson et al, 1982).
The significance of this finding is uncertain because the same study also found no
relationship between self-reported alcohol use and "foetal alcohol syndrome"
features. This is doubly surprising because of other evidence on the adverse effects of
alcohol, and because the epidemiological data indicates that cannabis and alcohol use
are associated (Norton and Colliver, 1988). An additional study reported an increase
in the crude rate of birth abnormalities among children born to women who reported
using cannabis. This result was no longer statistically significant after adjustment for
confounders (Linn et al, 1983), although the confidence interval around this adjusted
risk (OR 1.36) only narrowly included the null value (95 per cent CI: 0.97, 1.91).
The study by Zuckerman et al provides the most convincing failure to find an
increased risk of birth defects among women who used cannabis during pregnancy. A
large sample of women was obtained, among which there was a substantial
prevalence of cannabis use that was verified by urinalysis. There was a low rate of
birth abnormalities among the cannabis users, and no suggestion of an increase by
comparison with the controls. On this finding, one might be tempted to attribute the
small increased risk in the positive study (Linn et al, 1983) to recall bias, since the
report of cannabis use during pregnancy was obtained retrospectively after birth,
when women who had given birth to children with malformations may have been
more likely to recall cannabis use than those who did not. However, given the
uncertainty about the validity of self-reported cannabis use in many of the null
studies, it would be unwise to exonerate cannabis as a cause of birth defects until
larger, better controlled studies have been conducted.
— The health and psychological consequences of cannabis use, Hall (1994) [29]
Kan den cancerhämmande drogen cannabis orsaka cancer? Ja, det kan nog diverse
förbudsförespråkare inbilla befolkningen, men forskningen har inte kunnat hitta några starka bevis för
påståendet.
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