Some lessons can be distilled from our review. SUDs are classic complex traits with strong evidence supporting the etiological roles of both genetic or biological and environmental or social risk factors. Taking a ‘genes only’ perspective on SUDs will miss critical parts of the causal picture. We already know that a large proportion of risk genes for SUDs will not be substance specific in their effects but will rather predispose to addiction generally or even to broader externalizing traits. Genetic and environmental risks for SUD typically do not just add together but act and interact with each other during development. Generally, environmental factors are more important for initiation and less important for progression to dependence, whereas the reverse is seen for genetic factors.
