Source: British Menopause Society (BMS)

Progestogen administration is required to oppose naturally produced or administered estrogens to provide endometrial protection. Within HRT regimens, this should be delivered for at least the same duration as that produced during the luteal phase of the monthly cycle and in the recommended doses to protect against the risk of endometrial hyperplasia and endometrial cancer.

This includes progestogens administered for 12–14 days a month in sequential regimens and continuous daily intake in continuous combined HRT regimens. Studies have shown that shorter durations and lower doses of progestogen intake are likely to be associated with an increased risk of breakthrough bleeding, endometrial hyperplasia and endometrial cancer.