Phenotypic and genetic factors in motives for smoking.

Underlying phenotypic and genetic factors involving motives for smoking were assessed using data from 1756 twins, including 390 complete pairs. Respondents were aged 50 or older and included both current and former smokers. The Motives for Smoking Questionnaire (MSQ) hypothesizes eight correlated but distinct motives for smoking, which correspond to pharmacological and nonpharmacological second-order factors. This paper concentrates on the pharmacological motives. Principal-factor analysis recovered five categories. Items constituting Sedative, Stimulative, and Addictive reasons for smoking merged into one factor, whereas Automatic smoking, also considered to have pharmacological origins, formed a separate factor. Twin analysis was used to test for genetic effects and to determine whether these factors, although combined phenotypically, were affected by distinct genetic or environmental influences. Genetic effects accounted for a significant amount of the variance in the four hypothesized pharmacological motives for smoking, as did shared environment. The separate factor for Automatic smoking in the phenotypic analysis was due to environmental effects, and shared environment was a greater influence on Automatic smoking for women than men. One common effect explained the genetic variance; no genetic influence uniquely affected any specific motive. Therefore, individual differences in the hypothesized pharmacological motives for smoking appear to originate from a common genetic pathway.