There was a minimal increase in total genetic estimates for smoking from age 13–14 to age 19–20 (56% v. 60%). However, these effects decreased from age 13–14 to age 16–17. By contrast, examining the common genetic effects and smoking-specific genetic effects reveals a consistent trend, with common genetic effects decreasing and smoking-specific genetic effects increasing across development. Additionally, of all the substances, the cross-time continuity of the residual genetic effects was highest for smoking, with almost no new specific genetic effects estimated at age 19–20.
