THC has been found to inhibit reproductive function in the few human studies reported, although these studies have yielded inconsistent evidence. On the basis of research on animals it has been argued that cannabis would probably decrease fertility for both men and women in the short term. It has been suggested that in this respect the possible effects of cannabis use may be most significant for those males whose fertility is already impaired, for example those with a low sperm count. The results of research studies on the effects of prenatal cannabis use and birth outcome have been small and inconsistent. Some studies have suggested that cannabis smoking in pregnancy may reduce birth weight. A controlled study has found the relation between cannabis and birth defects has remained after controlling for any variables but this relation has not been found in other studies. So once again further research is much needed, in the meantime it is advisable that pregnant women avoid cannabis use. The effects of cannabis smoking where the study has found an association has been small compared to tobacco. There is little evidence that gestation is shorter except for adolescent mothers. Large well-controlled epidemiological studies have found no evidence that cannabis causes birth defects. Cannabis may have behavioural and developmental effects on infants exposed in utero during the first few months after birth. Between the ages of four and nine children who have been exposed to cannabis in utero have shown deficits in sustained attention, memory and cognitive functioning. However, the effects were small compared to tobacco and their clinical significance is unclear. The underlying causes might be the cannabis exposure or might be more closely related to the reasons underlying the mother’s use of cannabis during pregnancy. Recent case studies have found an increased risk of child cancers in children born to mothers who reported using cannabis during their pregnancies. However, cannabis was one amongst several factors considered in the analysis of the data from these studies and this area requires further study.
