BHRT Side Effects: Common Reactions, Serious Risks and When to Call

What are the most common BHRT side effects?

Bioidentical hormone replacement therapy (BHRT) uses estradiol and progesterone with the same structure as your own hormones. That structural match does not make side effects disappear: your tissues respond to estradiol and progesterone the same way whether they come from a patch, a pill, a compounded cream or your ovaries. Most early side effects reflect hormone levels that are a bit higher than your body is used to, or a dose that needs fine-tuning.

From estrogen

• Breast tenderness or swelling, the most common early complaint
• Bloating or fluid retention
• Headaches, especially if you were prone to hormonal headaches
• Nausea, more often with oral forms
• Skin irritation at patch or cream sites
• Vaginal discharge as tissue becomes better estrogenized

From progesterone

• Drowsiness or grogginess, which is why oral progesterone is usually taken at bedtime
• Mood changes, low mood or irritability in some women
• Bloating and breast tenderness
• Dizziness, mainly with oral doses

Bleeding

If you have a uterus, irregular spotting is common in the first months of combined therapy, especially when you start within a year or two of your last period. Sequential regimens cause a planned monthly bleed. Bleeding that is heavy, persists beyond the first few months, or starts after a stretch of none needs evaluation to rule out a problem with the uterine lining.

From testosterone, if prescribed

Acne, increased facial or body hair, scalp hair thinning and, at high doses, voice deepening or clitoral enlargement, which may not reverse. ACOG notes that the long-term effects of testosterone on heart disease and breast cancer risk in women are unknown (ACOG 2023).

How long do the side effects last?

Many early side effects ease within about 3 months as your body adjusts. Clinicians often schedule a check-in around then for that reason. If side effects are still bothersome, common fixes include:

For the flip side (when benefits typically show up), see how long BHRT takes to work.

Does BHRT cause weight gain or hair loss?

Randomized trials have not shown that estrogen therapy causes weight gain; early bloating and fluid retention can make the scale tick up for a few weeks. The shift toward more belly fat in midlife happens with or without hormones (see menopause weight gain). Hair is similar: thinning is common around menopause for many reasons, including thyroid problems and low iron. Estrogen and progesterone are not typical causes, but testosterone or high-androgen regimens can thin scalp hair in women who are prone to it.

What are the serious risks of BHRT?

Serious risks are uncommon for most healthy women in their 40s and 50s, but they are real, and "bioidentical" does not exempt anyone from them. The Menopause Society notes that risks differ by type, dose, duration, route, timing of initiation and whether a progestogen is used (Menopause Society 2022).

• Blood clots. In UK records of more than 80,000 women with clots, oral HRT was linked to higher risk (adjusted odds ratio 1.58), while transdermal estrogen was not linked to increased risk. Oral estradiol carried less risk than conjugated equine estrogens (Vinogradova 2019).
• Stroke. Oral estrogen slightly raises stroke risk, and the absolute risk climbs with age.
• Breast cancer. A worldwide analysis found all types of systemic HRT were linked to some excess breast cancer risk that rose with duration, more with estrogen plus progestogen than estrogen alone; vaginal estrogen was not (Collaborative Group 2019). In long-term Women's Health Initiative follow-up, estrogen alone after hysterectomy was associated with lower breast cancer incidence (Chlebowski 2020).
• Endometrial cancer. Estrogen without enough progestogen in a woman with a uterus raises the risk of endometrial hyperplasia and cancer. Oral micronized progesterone is the well-studied bioidentical option for protection. Progesterone absorbed from skin creams reaches low, variable blood levels, and whether that reliably protects the lining has long been debated (Stanczyk 2005), so bleeding on any regimen should be reported.
• Gallbladder disease, mainly with oral estrogen.
• Heart disease. Starting HRT more than 10 years after menopause or after 60 carries more risk; in younger, recently menopausal women, the Women's Health Initiative found low absolute risks (Manson 2013).

By the numbers

Blood clot risk depends on the route

1.58adjusted odds ratio for blood clots with oral HRTSource: Vinogradova 2019

No risein clot risk linked to transdermal estrogenSource: Vinogradova 2019

Are compounded bioidentical hormones riskier?

They aren't known to be safer, and they come with a few risks of their own. Compounded products are not FDA-approved, so their strength can vary between batches and pharmacies, and they lack the standard patient labeling that lists risks. There is also no requirement to report adverse events, which means side effect data are thin (ACOG 2023). Pellets add the risk of hormone levels that stay high for months and can't be reversed by removing the pellet; see hormone pellet side effects.

Who should not use BHRT?

When should you call a doctor?

Get urgent care for swelling, pain or warmth in one leg; chest pain or sudden shortness of breath; a sudden severe headache; changes in vision or speech; or weakness or numbness on one side of the body.

Contact your clinician soon for heavy or prolonged bleeding, new bleeding after months without it, a breast lump, yellowing skin or eyes, or a low mood that doesn't lift.

Do the benefits outweigh the risks?

For women under 60 or within 10 years of menopause who have no contraindications, The Menopause Society considers the benefit-risk balance favorable for treating bothersome hot flashes and preventing bone loss (Menopause Society 2022). Choosing transdermal estrogen when clot risk is a concern, using an appropriate progestogen if you have a uterus, and reviewing the plan yearly all help keep risks low. Our hormone replacement therapy guide walks through that decision.

If you're considering treatment, Amie's licensed clinicians can review your history online and, if appropriate, prescribe Amie HRT+, a compounded estradiol and progesterone cream. It is not FDA-approved. The clinician will tell you if an FDA-approved product or in-person care is a better fit, and you can reach the care team if side effects come up.

The bottom line