For females, the relative genetic contribution was lower, and the shared environmental contribution higher, for initiation of cannabis use as compared to problematic use, in accordance with Agrawal & Lynskey (43). This may be because the initial stages of the process of cannabis use are more sensitive to environmental factors, like drug availability and use by peers (52), whereas the likelihood of dependence is more influenced by biological factors such as individual differences in physical response to the drug.
