The prevalence of registration for cannabis, stimulant and sedative abuse in our entire sample of Swedish males born 1970–1990 (N = 1270,557), and in members of MZ and DZ twins, and near-age siblings are seen in Table 1. Cannabis abuse was most common followed by stimulant abuse and sedative abuse. The prevalences of all three of these forms of drug abuse were considerably lower in the two twin groups than in the general population or siblings, likely because the twins were screened for cooperativeness in having to return questionnaires about zygosity.
