Background: Postnatal depression can have long-term adverse consequences for the mother, for the marital relationship, and for the infant's psychological development. Such depressions can be severe and resistant to both support and counselling and to therapy with antidepressant drugs. We investigated the antidepressant efficacy of oestrogen given transdermally.

Methods: In a double-blind, placebo-controlled study, 61 women with major depression, which began within 3 months of childbirth and persisted for up to 18 months postnatally, were allocated randomly active treatment (n=34; 3 months of transdermal 17 beta-oestradiol 200 micrograms daily alone, then 3 months with added cyclical dydrogesterone 10mg daily for 12 days each month) or placebo (n=27; placebo patches and tablets according to the same regimen). The women were assessed monthly by self-ratings of depressive symptoms on the Edinburgh postnatal depression scale (EPDS) and by clinical psychiatric interview (schedule for affective disorders and schizophrenia [SADS]-change scale).

Findings: On pretreatment assessments the women in both groups were severely depressed (mean EPDS score 21.8 [SD 3.0] active group, 21.3 [2.9] placebo group; SADS scores, 66.3 [11.4] and 64.3 [10.7]). During the first month of therapy the women receiving oestrogen improved rapidly, and to a significantly greater extent than controls (mean EPDS scores 13.3 [SD 5.7] vs 16.5 [5.3]. Patients receiving placebo also improved over time but, on average, their scores did not fall below the screening threshold for major depression for at least 4 months. The estimated overall treatment effect of oestrogen on the EPDS was 4.38 points (95% Cl 1.89-6.87). None of a range of other factors (age, psychiatric, obstetric and gynaecological history, severity and duration of current episode of depression, and concurrent antidepressant medication), influenced the response to oestrogen.

Interpretation: This study has shown that transdermal oestrogen is an effective treatment for postnatal depression. Further studies are required to establish the minimum effective dose and shortest necessary duration of treatment as well as the mechanism of antidepressant action of oestrogen.