Oestrogen

Benefits

• reduces the severity and frequency of hot flushes by around 85%
• improves vaginal dryness
• by reducing menopausal symptoms, oestrogen may improve sleep and quality of life
• reduces the risk of post-menopausal bone fracture, including hip fracture
• not associated with weight gain
• may decrease the rsik of coronary heart disease

Side effects

• breast enlargement and tenderness
• nausea
• usually temporary
• may be dose related
• exacerbation of hormonally-sensitive migraine headache (only with oral)

Risks

• increased risk of blood clots (venous thromboembolism)
• increased risk of stroke 
• increased risk of gallbladder inflammation (cholecystitis)

Unopposed oestrogen

• Oestrogen stimulates the release of eggs from your ovaries and causes the cells of the womb lining to divide
• Progesterone gets the lining of your uterus ready to receive the egg from the ovaries
• The levels of oestrogen and progesterone in your body are usually balanced
• If oestrogen is not kept in check by progesterone, it can increase
• This is called unopposed oestrogen
• This unopposed oestrogen causes the cells of the endometrium (the lining of the uterus) to divide resulting in endometrial hyperplasia
• Endometrial hyperplasia is a condition in which the endometrium becomes abnormally thick.
• Although endometrial hyperplasia is not cancer, it can lead to uterine or womb cancer in some women
• Combining progestogen with oestrogen substantially reduces the risk of atypical endometrial hyperplasia
• Therefore, all patients with an intact uterus must be prescribed progesterone
• Approximately 20% of women given unopposed oestrogen for one year develop endometrial hyperplasia
• The risk persists for many years after oestrogen treatment has been stopped

 Oestrogen prescribing choices

• These formulations contain oestrogen only and are for patients with no uterus

Vaginal oestrogen to treat genitourinary syndrome of menopause can be prescribed alone or in addition to systemic HRT and does not require a progestogen for endometrial protection to be prescribed simultaneously.

https://jamanetwork.com/journals/jama/article-abstract/192323

https://jcp.bmj.com/content/54/6/435

https://www.nhs.uk/conditions/womb-cancer/causes/