Exclusions
Previous studies have demonstrated former depression to be the most
important risk factor for new depressions. Therefore, it is correct
primarily to exclude women with previous depression from such studies.
It makes no sense, however, to disregard the first four weeks of use of
HC and decide to classify this exposure period as non-exposed. Those who
experience mood changes by use of HC often report these symptoms within
days after starting this use, as demonstrated in study 1 and 2 which
followed women from start of HC exposure. That methodological decision
in study 3 will certainly underestimate the real risk of depression
development.
The other main difference between study 1 and 2 versus study 3 was the
exclusion of all women having used HC before turning 15 years. Thereby,
the age groups with the highest sensitivity for depression development
with HC use were excluded. Many of these women would have started use of
antidepressants after turning 15 years, while still being exposed to HC.
Exclusion of this group will thus also underestimate the risk of
depression development.
Finally, women who in addition to a depression also were recorded with
an anxiety diagnosis or use of anxiolytics at the same time as being
prescribed antidepressants, were excluded in study 3, also a
circumstance which would diminish the risk of depression development, as
this condition, especially in young women, is often associated with
anxiety disorders.
These three methodological circumstances are likely the main reason for
the discrepancies in results between study 1 and 2 versus study 3.