The effect of oral contraceptives on plasma cortisol and cortisol binding capacity throughout the menstrual cycle in normal women.

Plasma cortisol and cortisol binding capacity (CBC) was measured throughout the menstrual cycle in 25 healthy women aged between 20 and 35 years. Ten women were taking an oral contraceptive containing 50 mug oestrogen and progestogen ("combined pill"), one patient took a progestogen-only contraceptive and 14 served as controls. Despite the low oestrogen content of the combined pill the level of plasma cortison and CBC were signifcantly higher than in controls at all stages of the cycle, and the cortisol/CBC ratio greater than unity during most of it. Levels in the women taking a progestogen-only contraceptive were indistinguishable from controls. The plasma cortisol and CBC levels were significantly higher in the last week of the cycle than in the first in the combined pill group, but there was no significant variation in the controls.