The picture for environmental effects was slightly different for illicit drugs. Total shared environmental effects were the same at ages 13–14 and 19–20 (13%). However, these effects doubled (26%) at age 16–17. Additionally, a majority of the shared environmental effects were accounted for by the common factors. Total unique environmental estimates decreased minimally across the ages whereas common estimates increased. Specific unique environmental estimates dropped sharply from age 13–14 (13%) to age 16–17 (2%) and 19–20 (1%) and no cross-time continuity was revealed.
