The Ottawa Prenatal Prospective Study has monitored the effects of prenatal marijuana exposure on the cognitive function of children since 1978.14 So far the study has failed to find evidence that children whose mothers smoked marijuana during pregnancy perform below average on a variety of intelligence tests. Some early cognitive problems were detected among children of women who smoked at least one joint per day during pregnancy, but these deficits were no longer apparent after the children reached age 5. Older children of marijuana users did, however, score slightly lower than those of both nonsmokers and tobacco smokers on tasks that measured their ability to plan ahead and control self-defeating behavior. On the other hand, children whose mothers smoked tobacco during pregnancy scored somewhat lower on tests of language and cognitive skills than the other two groups and continued to do so as late as age 12. In most cases the differences in test scores between groups of comparable children varied by less than 5 percent; thus, the effects, while statistically significant, are subtle.
In summary, there are many reasons to worry that for people who might choose to use marijuana as medicine—and especially those who smoke it—the drug could actually add to their health problems. Proof that habitual marijuana smoking does or does not lead to respiratory cancer awaits the results of extensive, carefully designed epidemiological studies. In the meantime it appears that, for people with chronic medical disorders or those with compromised respiratory or immune systems, smoking marijuana is likely to do more harm than good. Likewise, for people at risk of cardiovascular disease, pregnant women, and couples trying to conceive, the potential risks of either THC or smoked marijuana appear to exceed the potential medical benefits.
The most talked about health risk associated with marijuana is its potential to promote abuse and addiction. There is great disagreement on this topic and scant evidence that applies specifically to marijuana used solely to relieve medical symptoms. Nevertheless, research from a variety of perspectives—including