Introduction
Over recent years, three Nordic large-scale epidemiological studies have
tried to quantify the influence of use of different types of hormonal
contraceptives on the risk of developing depression or use of
antidepressant drugs1-3. In the following, the first
Danish study1 is called “study 1”, the first Swedish
study2 “study 2”, and the second Swedish
study3 “study 3” according to time of publication.
Although at first sight these three studies seem rather similar in
methods, the authors of these three studies – surprisingly - made quite
different conclusions from their findings, although some results were
similar in all three studies. Going into details on the methods,
however, may reveal differences which might explain the different
findings and conclusions.
The issue is important, because hormonal contraception (HC) is one of
the most frequent medical exposures worldwide, and depression or use of
antidepressants are among the most frequent outcomes in the same
countries.
The aim of this study was to compare the three studies and explore
whether differences in methods may explain the different results, and
whether ideological differences towards hormonal contraception also may
play a role for the chosen methods and the interpretation of the
results.