Hormone replacement therapy (HRT)

HRT consists of oestrogen and progesterone replacement, using natural oestrogens derived from horse urine, and progestogens:
• oestradiol
• oestrone
• oestriol.
Conjugated oestrogens is the term given to a combination of natural oestrogens. There are synthetic oestrogens available, these are:
• ethinyloestradiol
• mestranol
• diethylstilboestrol.

Progesterons includes:
• progesterone
• didrogesterone
• hydroxyprogesterone
• medroxyprogesterone
• norgestrel and derivatives.

Progestogens are normally prescribed with oestrogens as a tablet to be taken in the second half of the monthly cycle, because oestrogens cause the womb-lining to over thicken if taken on their own and this carries a high risk of cancer. These hormones are supplied in much larger amounts than the body’s natural (endogenous) production, to offset losses through digestion and tissue dispersal.

How HRT works
HRT preparations replace endogenous (a woman’s own) hormones. They act on peripheral tissues (target cells) but they send negative feedback to the hypothalamus, which reduces the production of releasing and stimulating factors. Side effects occur because they are given in higher doses than endogenous hormones and they disrupt the fine-tuning of the positive and negative feedback processes.