A large international working group analysed data from the World
Health Organization on surveys carried out in 17 countries on
different continents. The data did not support the gateway theory
according to which the use of certain drugs (cannabis, tobacco,
etc.) leads to the use of harder drugs, which "implies that
successful efforts to prevent use of specific 'gateway' drugs may
not in themselves lead to major reductions in the use of later
drugs." (Source: Degenhardt L, et al. Drug Alcohol Depend, 2010
Jan 7. [Electronic publication ahead of print])