to 70% for cannabis abuse. Fourth, estimates for total shared environmental contributions to the three classes of DA were more modest and quite similar: 20% for stimulant abuse and 18% for both cannabis and sedative abuse. Fifth, substance specific gene effects were seen for all three classes of substances. Such effects were largest for cannabis – accounting for 24% of total genetic influences – and smallest for stimulants where the parallel figure was 8%. Finally, in contrast to the pattern for genetic effects, no substance specific shared environmental effects were detected. All of the shared environmental influences on cannabis, stimulant and sedative abuse were, in this model, estimated to derive from the common latent factor.
