During a woman's reproductive years, her ovaries produce hormones known as oestrogen and progesterone. Oestrogen regulates her monthly menstrual cycle and secondary sexual characteristics such as breast function and development. It peaks at different times in the menstrual cycle to ensure her body is prepared for fertilisation and reproduction.

Progesterone also peaks to prepare the woman's uterus for potential pregnancy and her breasts for lactation. However as a woman approaches the menopause which is usually around the age of 50, her body produces less oestrogen and progesterone. Experts have predicted that 40 million women will experience the menopause in the next 20 years.

The decrease in oestrogen in menopause can create uncomfortable symptoms such as hot flashes, vaginal dryness, sleep disturbance and many more irritable effects.

The dryness of tissue around the vagina and urethra can be uncomfortable or even painful during sexual intercourse and urination. Hormone Replacement Therapy can help relieve these symptoms and other menopausal problems. Hormone Replacement therapy (HRT) is a synthetic oestrogen and progesterone, known as progestin which are designed to replace a woman’s declining hormones.

Previous research has indicated that HRT can also prevent osteoporosis, hear disease, depression, short term memory loss and other diseases in post-menopausal women. However, more recent research has shown that HRT might not provide such benefits and may create other risks including an increased risk of ovarian cancer with prolonged use, and cancer of the uterine lining for those women who do not take progestin with oestrogen.
Although HRT is effective at relieving menopausal symptoms and possibly provide a protection again certain conditions such as osteoporosis, there is also evidence to suggest there is a link between HRT and the increased risk of breast caner.

During July 2002, a large study on HRT was halted by the National Institute of Health. It was found that the combined oestrogen and progestin regimen of the therapy was the cause of eight cases of invasive breast cancer for every 10,000 women taking HRT. This was a 26% increase in breast cancer risk compared to those women who were not taking HRT.

Experts believe that although these numbers appear to be alarming, short term use or HRT can be safe amongst those women who are not at high risk of developing breast cancer or other diseases. This indicates the importance of patients of physicians making the decision about HRT based on their individual medical situation and family history.

As mentioned above, oestrogen and progestin are the two hormone supplements that are the most used for HRT. If one was to take oestrogen without progestin to balance the hormonal cycle, you could cause over stimulation of the endometrium tissue which is more commonly known as the lining of the uterus. This has found to lead to uncontrolled tissue growth known as hyperplasia leading to endometrial cancer.

Progestin can counteract this risk. Therefore those women who still have their uteruses are more commonly prescribed oestrogen and progestin together. Progestin can be prescribed by itself to prevent hot flashes and other menopausal problems.