From Maia Szalavitz
David Fergusson was quoted as saying that he “can’t explain away” the
correlation between marijuana use and subsequent hard drugs use found in his
study in New Zealand. But the hardly radical Institute of Medicine, part of the
US National Academy of Sciences, discredited the “gateway theory” that marijuana
leads to hard drugs use in its recent report to Congress on the potential
dangers of medical marijuana. The report said, “There is no conclusive evidence
that the drug effects of marijuana are causally linked to the subsequent abuse
of other illicit drugs.”
Even Fergusson’s paper qualifies his comments more than your reporter
suggests. His abstract ends with the statement: “Findings support the view that
cannabis may act as a gateway drug that encourages other forms of illicit drug
use. None the less, the possibility remains that the association is non-causal
and reflects factors that were not adequately controlled in the analysis.”
Let me suggest just one major confounding factor. Perhaps some people simply
like taking drugs, and some of those people like to take them more often than
others and like to try many different ones. This could explain why two-thirds of
cannabis smokers don’t use other drugs—and why heavier smokers are more
prone to use other drugs—better than any pharmacological idea about pot
changing the brain. Occam’s razor needs to be applied with particular sharpness
to research on illicit drugs, which tends to serve political agendas far more
than scientific ones.
New York
