The Critical Oestrogen Content of Combined Oral Contraceptives

Abstract

A review of the evidence concerning efficacy, safety and side-effects of oral contraceptives indicates clear differences related to the lowering of oestrogen dosage. It is suggested that 50 μg of ethinyloestradiol or its equivalent is a critical dose, for below that level the efficacy in combination with current progestogens falls almost twenty-fold without evidence of a similar reduction in unwanted side-effects.

In fact there is a marked increase of irregular bleeding patterns in early cycles associated with diminished patient acceptance.