Association between antidepressant resistance in unipolar depression and subsequent bipolar disorder: cohort study

People with major depressive disorder who fail to respond to adequate trials of antidepressant treatment may harbour hidden bipolar disorder. We aimed to compare the rates of a change in diagnosis to bipolar disorder among people with major depressive disorder with stratified responses to antidepressants during an 8-year follow-up period. Information on individuals with major depressive disorder identified during 2000 (cohort 2000, n = 1485) and 2003 (cohort 2003, n = 2459) were collected from a nationally representative cohort of 1,000,000 health service users in Taiwan. Participants responding well to antidepressants were compared with those showing poor responses to adequate trials of antidepressants. In 7.6-12.1% of those with a diagnosis of unipolar major depressive disorder this diagnosis was subsequently changed to bipolar disorder, with a mean time to change of 1.89-2.98 years. Difficult-to-treat participants presented higher rates of change to a bipolar diagnosis (25.6% in cohort 2000; 26.6% in cohort 2003) than easy-to-treat participants (8.8-8.9% in cohort 2000; 6.8-8.6% in cohort 2003; P