In women receiving estrogen replacement therapy there is an increased risk of endometrial cancer which can be countered by progesterone administration.
Patient information leaflets are here:
Oestrogel: Apply the amount of gel prescribed by your doctor once a day either in the morning or evening to either each shoulder, outer arm or each mid-inner thigh.
Utrogestan: The recommended dose is 200 mg daily at bedtime, for twelve days in the last half of each therapeutic cycle (beginning on Day 15 of the cycle and ending on Day 26). Withdrawal bleeding may occur in the following week.
Alternatively 100 mg can be given at bedtime from Day 1 to Day 25 of each therapeutic cycle, withdrawal bleeding being less with this treatment schedule.