This is the “weakest” form of estrogen.

Compared to conventionalpharmaceuticalestrogens that typically make use of just estradiol, this is generally safer to use.

Initially, it was deemed insignificant because of the weak estrogenic activity. However, over time, it has proven to be of use in treating various conditions.

Studies have shown that it is highly effective in mitigating symptoms of menopause. In particular, it can reduce occurrences of hot flashes and vaginal dryness.

Ironically, it being the weaker form may be its strongest suit because topical formulations of estriol do not increase the risk of cancers associated with hormonal therapy such as breast or endometrium cancer.

Estriol is great for the skin and mucous membranes, and its topical application can help increase collagen and hydrate cells. And thus, it’s very effective in menopausal women who deal with painful intercourse due to physiological changes like vaginal dryness and vaginal atrophy.

Recent research indicates that estriol has beneficial effects on bone mineral density. Estrogen has a role in bone formation, and thus many elderly women suffer from problems like osteoporosis which predisposes them to fractures even after trivial trauma.

Interestingly in the same study that showed its link to better bone mineral density, it was also found that estriol may lower total cholesterol levels and enhance High-Density Lipoprotein (HDL) levels (the "good" cholesterol).

While more research is necessary in this regard, the findings so far suggest that treatment with estriol is associated with a decrease in blood pressure.

The above findings suggest that estriol may have beneficial effects on cardiovascular health.

It is also beneficial for postmenopausal women who suffer from recurrent urinary tract infections. A randomized controlled trial found that this form of estrogen can improve symptoms of urinary incontinence and can reduce the recurrence of UTI.

It is available in various formulations such as tablets, creams, and suppositories over-the-counter.

Side effects include weight gain, migraine, edema, breast tenderness and pain, fatigue, bloating, changes in menstrual bleeding, and upper respiratory tract infections.

Additionally, it can cause spotting and periods. Those who take it may also experience moodiness.

Estradiol is the most potent form of estrogen that is typically used in hormone replacement therapy (HRT).

It is available in the form of oral tablets, transdermal gels, creams or, patches. It is also available in the form of injections.

Since its primary use is to reduce menopausal symptoms that manifest in the vagina, such as dryness and itching, it can be administered locally.

Similar to estriol, it is excellent in improving bone mineral density and preventing urinary tract infections.

It can help in relieving menopausal symptoms such as night sweats and hot flashes.

It also enhances vaginal secretions and thus lubrication during sexual intercourse.

Additionally, research has also shown that both (estriol and estradiol) are beneficial in maintaining neurological health.

It is also available in various formulations such as tablets, creams, transdermal patches, and suppositories over-the-counter.