Progesterone only pill
The progesterone only oral contraceptive pill (minipill) contains progesterone but unlike the combined pill it does not contain oestrogen. When produced naturally, progesterone renders the endometrium suitable for implanting of a fertilized ovum and inhibits further release of GRH, FSH, and LH so regulates cycle and ovulation. If no fertilization takes place the corpus luteum regresses and progesterone levels drop so the endometrium cannot be maintained and menstruation occurs. Lack of progesterone also means the clamp on GRH, FSH and LH secretion is released.
The progesterone only pill is mainly effective due to its effect on cervical mucus, it doesn't actually stop ovulation.
If taken regularly it can cause irregular periods and it is considered less effective than the combined pill.
It is said to have a number of side effects including:
- weight gain
- mild nausea
- skin changes e.g. acne
- blood clots