Factors associated with switching and combination use of antidepressants in young Swedish adults

Little is known on factors associated with switching and combination use of antidepressants. Our aim was to describe such use and to analyse the association with socioeconomic factors and level of care in Swedish adults aged 20-34 years.

Individuals, aged 20-34 years, who purchased an antidepressant in January-June 2006, and who had not purchased any antidepressant in the preceding 6 months (n = 24,897) were followed from 6 up to 12 months. Among those who purchased ≥ 2 antidepressant substances, switchers were defined as those who did not fulfil the requirements for combination use. Data on purchased antidepressants and socioeconomic characteristics were obtained from the Swedish Prescribed Drug Register and Statistics Sweden. The association between (i) ≥ 2 antidepressants or (ii) switching, respectively, and socioeconomic factors as well as level of care was analysed with multiple logistic regression.

A total of 4254 individuals (17%) purchased ≥ 2 antidepressant substances, and the remaining 20,643 (83%) purchased one antidepressant. The adjusted odds ratio (OR) for purchase of ≥ 2 antidepressants (vs. purchase of one antidepressant only) was higher among those who started on mirtazapine compared with selective serotonin re-uptake inhibitors: 2.23 (95% confidence interval: 1.93-2.57), and lower in individuals with high education: 0.64 (0.54-0.75), and shorter length of follow-up: 0.73 (0.62-0.85). Among those with ≥ 2 antidepressants, 71.6% were classified as switchers. The adjusted OR for switching (vs. combination use) were higher among divorced/widows/widowers: 1.61 (1.05-2.49), and lower among individuals with short university education: 0.58 (0.43-0.78), those starting on mirtazapine: 0.78 (0.62-0.97), and when treatment was initiated in psychiatric care: 0.75 (0.63-0.88).

One of six new users purchased at least two antidepressants, the majority were classified as switchers. Purchase patterns were associated with socioeconomic characteristics, in particular level of education, type of first purchased antidepressant, and level of care initiating treatment.