Estriol

Estriol (oestriol) is a naturally occurring, weak oestrogen used primarily as a topical treatment for the vaginal and urinary symptoms of the genitourinary syndrome of menopause (GSM), formerly known as atrophic vaginitis. Available in the UK as Ovestin cream and pessaries, it delivers targeted local oestrogen therapy to restore the health of the vaginal tissues without the level of systemic exposure associated with conventional systemic HRT.

Why Localised Oestrogen Matters

As oestrogen levels decline around and after the menopause, the tissues lining the vagina, urethra, and bladder base become thinner, drier, and more fragile, a condition that affects around half of all postmenopausal women. Symptoms include vaginal dryness, burning, discomfort during intercourse, increased susceptibility to vaginal infections, and urinary symptoms such as urgency, frequency, and recurrent urinary tract infections. Unlike systemic HRT, which raises oestrogen levels throughout the body, estriol cream or pessaries act locally, restoring tissue health in the target area with very low levels of systemic absorption. This makes it suitable for many women who cannot or prefer not to use systemic HRT.

Oestriol Compared to Other Local Oestrogens

Oestriol is considered the weakest of the three main naturally occurring oestrogens, alongside oestradiol and oestrone. Because of its lower binding affinity for oestrogen receptors and its predominantly local action, it is less likely to stimulate endometrial tissue even when used without a progestogen. Long-term use at the recommended dose has not been associated with an increased risk of endometrial hyperplasia, which distinguishes it from stronger systemic oestrogens. Women with a history of hormone-sensitive conditions should nonetheless discuss use with their prescriber before starting treatment.

Estriol cream (Ovestin) is applied intravaginally using the applicator provided with the product. Estriol pessaries are inserted directly into the vagina, also using the applicator supplied.

Initial and Maintenance Treatment

During the first two to three weeks of treatment, estriol is typically used daily to rapidly restore vaginal tissue health and relieve acute symptoms. Once the tissue has responded and symptoms have improved, usually after two to four weeks, the frequency is reduced to twice weekly for maintenance. This twice-weekly maintenance dose should be continued long-term to sustain the benefit, as symptoms recur if treatment is stopped. Apply or insert the preparation at bedtime to minimise leakage and allow optimal contact time with the vaginal mucosa.

Practical Application Tips

Use the graduated applicator to measure the correct amount of cream (0.5g) and insert it gently into the vagina while lying down. Wash the applicator with warm water and mild soap after each use. For pessaries, insert one pessary as high into the vagina as is comfortable using the applicator or your finger. Light spotting or a small amount of discharge is normal during initial treatment. If you experience significant bleeding, stop using the preparation and consult your GP promptly.

The standard adult dose of estriol cream (Ovestin) is 0.5g intravaginally once daily for two to three weeks during the initial phase, reducing to 0.5g twice weekly for ongoing maintenance. Each 0.5g dose delivers 0.5mg of oestriol.

Estriol pessaries (Ovestin 0.5mg) are used on the same schedule: one pessary daily for two to three weeks, then one pessary twice weekly for maintenance.

Some women are prescribed a shorter initial phase of one to two weeks if symptoms are mild. The maintenance dose should be the lowest that keeps symptoms controlled. Estriol products do not require dose adjustment for mild to moderate kidney or liver impairment, but these conditions should be disclosed to the prescribing clinician. There is currently no established safety data for use in children, and estriol is not indicated outside the postmenopausal indication.

Common Side Effects

• Vaginal discomfort, burning, or irritation, particularly during the initial treatment phase
• Vaginal discharge or increased moisture
• Mild vaginal bleeding or spotting (usually resolves within a few weeks)
• Breast tenderness
• Vulval irritation or itching
• Headache or mild nausea (rare with local application)

Serious Side Effects

• Unexpected or heavy vaginal bleeding, stop treatment and consult your GP urgently
• Allergic reaction to the formulation components (itching, rash, swelling)
• Signs of systemic oestrogen effects (breast lump, worsening migraines) if used in high frequency beyond prescribed schedule
• Endometrial stimulation with prolonged high-frequency use beyond the recommended dose

Use in Women with Hormone-Sensitive Conditions

While the systemic absorption of estriol from vaginal preparations is low, it is not zero. Women with a personal history of breast cancer, endometrial cancer, or other oestrogen-sensitive malignancies should consult an oncologist or specialist before using any vaginal oestrogen preparation, including estriol. Some breast cancer treatment guidelines conditionally permit the use of vaginal oestrogen in women on aromatase inhibitors when quality of life is significantly affected; this decision must be made collaboratively.

Monitoring and Long-Term Use

Women using estriol long-term should attend regular gynaecological review. Any vaginal bleeding that occurs beyond the initial treatment phase requires prompt medical assessment to exclude endometrial pathology. Although oestriol at the recommended dose has not been shown to cause endometrial hyperplasia, current guidance recommends annual review for all women on vaginal oestrogen therapy. Women with known endometriosis should be monitored carefully, as reactivation of the condition has been reported with local oestrogen use. Keep estriol preparations out of reach of children and store at room temperature.

• Known, suspected, or previous oestrogen-dependent malignancy, including breast and endometrial cancer (unless under specialist review)
• Unexplained vaginal bleeding
• Untreated endometrial hyperplasia
• Active or recent venous thromboembolism (seek medical advice; risk is lower with local vs. systemic oestrogen)
• Active liver disease or severe hepatic impairment
• Pregnancy or breastfeeding
• Known hypersensitivity to oestriol or any excipient in the preparation
• Porphyria