Genetics (TAG) Consortium may be the most relevant for the phenotype of heroin addiction; in a previous study [42], PRS for cigarettes per day had predicted the number of glasses of alcohol consumed per day and age at onset of smoking predicted age at regular drinking. In the current study, no smoking phenotypes studied (ever smoked, cigarettes per day, former smoker, age of onset for smoking) predicted heroin addiction, when using the suggested significance threshold of α = 0.001; instead, there was a suggestive relationship with ‘ever smoked’ and age at first cigarette. The proportion of variance in heroin use explained by polygenic risk score was very low or moderately low (Nagelkerke’s R2 = 0.001–0.06) for all the phenotypes tested (Figure B(i)-(iv) in S1 File).
