Cholesterol-lowering drugs and antidepressants - A study of prescription symmetry

The subject of this study was to investigate the relationship between presc ription of cholesterol-lowering drugs and depression. We used prescription of antidepressants as a proxy for depression and analysed the prescription order for cholesterol-lowering and antidepressant drugs. The ratio of perso ns with antidepressants prescribed second and first translates directly int o a rate ratio (RR) associating cholesterol-lowering drugs use with antidep ressants. The crude RRs were then adjusted for trends in sales of the drugs over the study period. All residents of Funen, Denmark, who started the tw o therapies during the period I April 1991 through 31 December 1995 were in cluded in the study cohort. Of 184 individuals included in the analysis, 10 5 started antidepressant first and 79 second, giving a crude RR of 0.75. Ho wever, the sales of cholesterol-lowering drugs increased more than the sale s of antidepressants. Accordingly, the adjusted RR was higher than the crud e, 0.90 (95% confidence interval 0.68 to 1.22). Among three tested choleste rol-lowering drug classes, only simvastatin showed an adjusted RR above uni ty (1.59, 95% confidence interval 1.08 to 2.45). The hypothesis that the us e of cholesterol-lowering drugs has an adverse effect on mood is not suppor ted by the present study. Confounding by indication might explain the appar ent association between use of simvastatin and antidepressants. (C) 1998 Jo hn Wiley & Sons, Ltd.