What medications affect estrogen levels?

October 10, 2025 •

5 min read

Over 70% of breast cancers have estrogen receptors and rely on the hormone to grow, making medications that affect estrogen levels a critical component of treatment. Beyond cancer therapy, many other prescriptions, from hormonal contraceptives to mood stabilizers, can intentionally or unintentionally alter the body's delicate estrogen balance. Understanding these pharmacological effects is vital for managing various health conditions and navigating potential side effects.

Quick Summary

This article explores different classes of medications that intentionally or unintentionally influence estrogen levels. It covers drugs that increase estrogen, like hormone replacement therapy and contraceptives, as well as those that decrease it, such as aromatase inhibitors and GnRH agonists. The article also details the selective action of SERMs and discusses the less-obvious impacts of other prescriptions on hormonal balance.

Key Points

Increase Estrogen: Hormone replacement therapy and combined hormonal contraceptives directly increase or stabilize estrogen levels to treat menopause symptoms, contraception, or estrogen deficiency.
Decrease Estrogen: Aromatase inhibitors, GnRH agonists, and SERDs are used to lower estrogen levels to treat hormone-sensitive cancers like breast cancer and conditions like endometriosis.
Modulate Receptors: Selective Estrogen Receptor Modulators (SERMs) act differently depending on the tissue; for example, tamoxifen blocks estrogen in breast tissue but acts like estrogen in the uterus.
Unintended Effects: Certain non-hormonal medications, including some antidepressants and antiepileptic drugs, can unintentionally influence estrogen metabolism or signaling.
Herbal Caution: Herbal supplements containing phytoestrogens may mimic estrogen, but their potency and safety are not standardized, requiring caution and medical consultation.
Consult a Doctor: Given the complex and varied effects of these medications, consulting a healthcare provider is essential for understanding risks and managing hormonal changes associated with any prescribed or over-the-counter treatment.

Medications That Increase Estrogen

Medications designed to increase estrogen are most commonly used in hormone replacement therapy (HRT) for managing menopausal symptoms or addressing estrogen deficiency. These drugs directly supplement the body with estrogen or mimic its effects. For women with an intact uterus, estrogen must be combined with a progestin to protect the uterine lining from potential overgrowth.

Estrogen-Only Therapy: Available in oral pills, skin patches, gels, sprays, and vaginal products, this is primarily for women who have had a hysterectomy. Examples include conjugated estrogens (Premarin) and various estradiol products (Vivelle-Dot, Estrace).
Combination Hormone Therapy (Estrogen + Progestin): Combining estrogen with a progestin is essential for women with a uterus to prevent endometrial cancer. This can be administered via pills, patches (Combipatch), or even an intrauterine device.
Hormonal Contraceptives: Combination birth control pills, patches, and vaginal rings contain synthetic estrogen (ethinyl estradiol) and progestin. They work by preventing ovulation and stabilizing hormone levels, but doses vary widely. Low-dose pills are available for those sensitive to estrogen side effects.

Medications That Lower Estrogen

Conversely, many medications are designed to decrease estrogen levels or block its effects, often for treating hormone-sensitive conditions like breast cancer and endometriosis.

Aromatase Inhibitors (AIs): This class of drugs blocks the aromatase enzyme, which converts other hormones into estrogen. AIs are effective in postmenopausal women whose ovaries no longer produce significant estrogen. Examples include anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin).
Gonadotropin-Releasing Hormone (GnRH) Agonists and Antagonists: These medications work by shutting down the ovarian production of estrogen, effectively creating temporary menopause. They are used for advanced breast cancer and endometriosis. Examples include goserelin (Zoladex), leuprolide (Lupron), and elagolix (Orilissa).
Selective Estrogen Receptor Degraders (SERDs): A newer class of antiestrogen therapy, SERDs bind to and degrade estrogen receptors. Fulvestrant is an example, given as a monthly injection.

Selective Estrogen Receptor Modulators (SERMs)

SERMs are a complex class of drugs that can act as either estrogen agonists (mimicking estrogen) or antagonists (blocking estrogen) depending on the specific tissue. This tissue-specific action allows for targeted therapy with fewer systemic side effects than traditional hormone therapies.

Tamoxifen: Often considered the prototypical SERM, tamoxifen is a powerful estrogen antagonist in breast tissue, making it a cornerstone for treating and preventing hormone receptor-positive breast cancer. However, it has an estrogen-like effect on the uterus, which can increase the risk of endometrial cancer with long-term use.
Raloxifene (Evista): This SERM is used for preventing and treating osteoporosis in postmenopausal women. It acts as an estrogen agonist on bone to maintain density but is an antagonist in breast and uterine tissue, avoiding the endometrial risks associated with tamoxifen.
Ospemifene (Osphena): This SERM has estrogenic effects on vaginal tissue, making it useful for treating painful sexual intercourse and vaginal dryness in postmenopausal women.

Other Medications with Unintended Hormonal Side Effects

Certain medications, not primarily intended for hormonal regulation, can still affect estrogen levels indirectly.

Antidepressants (SSRIs): Some selective serotonin reuptake inhibitors (SSRIs), like fluoxetine and sertraline, have been shown to influence estrogen levels, although the effects can be inconsistent. High doses may disrupt the estrous cycle in animal studies and alter uterine estrogen signaling. Women taking these medications should discuss potential hormonal side effects with their healthcare provider.
Antiepileptic Drugs (AEDs): Enzyme-inducing AEDs such as carbamazepine and phenytoin can increase the metabolism of estrogen and other sex hormones, potentially decreasing their effectiveness, particularly in women on oral contraceptives. Other AEDs like valproate can increase serum testosterone, leading to hormonal imbalances.
Herbal Supplements: Some herbal remedies, such as black cohosh, red clover, and chasteberry, contain phytoestrogens—plant-derived compounds that can mimic estrogen in the body. While sometimes marketed for menopausal symptom relief, they are not FDA-regulated, and their purity, potency, and long-term effects are often uncertain.

Comparison of Estrogen-Affecting Drug Classes


Drug Class	Primary Purpose	Mechanism of Action	Effects on Estrogen	Common Examples
Hormone Replacement Therapy (HRT)	Relieve menopausal symptoms, treat estrogen deficiency	Directly provides the body with estrogen (and often progestin) to supplement or replace natural hormone levels.	Increases/replaces circulating estrogen.	Estradiol (patches, gels), conjugated estrogens (Premarin).
Hormonal Contraceptives	Prevent pregnancy, manage endometriosis	Contain synthetic estrogen and progestin to suppress ovulation and stabilize hormone levels.	Increases/stabilizes circulating estrogen levels.	Combination pills, patches, rings.
Aromatase Inhibitors (AIs)	Treat hormone receptor-positive breast cancer	Blocks the aromatase enzyme, preventing the conversion of androgens into estrogen.	Significantly decreases total estrogen levels, especially in postmenopausal women.	Anastrozole (Arimidex), letrozole (Femara).
Selective Estrogen Receptor Modulators (SERMs)	Treat breast cancer, prevent osteoporosis	Act as estrogen agonists or antagonists depending on the tissue type.	Blocks estrogen action in some tissues (breast) while mimicking it in others (bone).	Tamoxifen, raloxifene.
GnRH Agonists/Antagonists	Treat endometriosis, advanced breast cancer	Suppress ovarian estrogen production by disrupting signals from the brain.	Significantly decreases circulating estrogen levels.	Goserelin (Zoladex), leuprolide (Lupron), elagolix (Orilissa).

Conclusion

Numerous medications, both hormonal and non-hormonal, can significantly impact a person's estrogen levels, with important implications for treatment outcomes and side effect profiles. Estrogen-based medications are used for hormone replacement and contraception, while anti-estrogen drugs like aromatase inhibitors and SERDs are crucial for treating hormone-sensitive cancers and endometriosis. The selective actions of SERMs like tamoxifen and raloxifene offer targeted therapeutic benefits but also carry specific risks related to their tissue-specific effects. Furthermore, certain classes of drugs, such as antidepressants and antiepileptics, can have unintended and complex effects on hormonal balance through interactions with metabolic pathways or the central nervous system. Given the wide array of potential interactions and side effects, it is essential for individuals to consult with a healthcare provider to understand how any medication, prescription, or supplement might affect their estrogen levels. Informed medical guidance ensures that the benefits of treatment outweigh any potential risks associated with hormonal changes.

How Tamoxifen Works and Its Implications

Tamoxifen's dual role as an estrogen antagonist in breast tissue and a partial agonist in the uterus is a prime example of a SERM's complex action. It binds to estrogen receptors in breast cells, blocking estrogen from stimulating cancer cell growth. However, it can promote uterine cell growth, leading to an increased risk of endometrial cancer, a crucial factor in long-term treatment decisions. For more detailed information on how these drugs function, the National Institutes of Health offers extensive resources.

Potential side effects of estrogen-affecting medications

Estrogen-based HRT: May increase the risk of blood clots, strokes, and heart disease, with risk factors influenced by age and time since menopause.
Aromatase Inhibitors: Potential side effects include joint pain, muscle pain, and accelerated bone loss due to significant estrogen reduction.
SERMs (Tamoxifen): While reducing breast cancer risk, long-term use is associated with a slightly increased risk of endometrial cancer and blood clots.
Antidepressants (SSRIs): Some studies suggest a link to sexual dysfunction and potential disruptions in hormone signaling, though findings are mixed.
Antiepileptic Drugs (AEDs): Enzyme-inducing AEDs can reduce the effectiveness of oral contraceptives, while others like valproate may increase testosterone levels in women.

Managing treatment

Talk to your doctor: Discuss your complete medical history and all medications or supplements you take to ensure safe and effective treatment, especially if you have a history of hormonal cancers, blood clots, or other chronic conditions.
Monitor side effects: Stay vigilant for any side effects and report them to your doctor. For instance, women on AIs may need regular bone density scans.
Consider low-dose options: For hormonal contraceptives, low-dose options exist that may reduce estrogen-related side effects.
Address hormonal shifts: For medications with unintended hormonal side effects, your doctor may suggest adjustments or alternative treatments to manage any changes.

Frequently Asked Questions

Combination birth control pills increase or stabilize estrogen levels by adding synthetic estrogen to the body, which, along with progestin, helps prevent ovulation.

Many breast cancers are hormone-receptor-positive, meaning they use estrogen to grow. Medications like aromatase inhibitors lower the body's overall estrogen supply to starve the cancer cells.

A simple estrogen blocker, like an aromatase inhibitor, lowers the body's total estrogen levels. A SERM selectively acts as either an estrogen agonist (mimic) or antagonist (blocker) depending on the tissue type, allowing for targeted effects.

Yes, some antidepressants, particularly SSRIs like fluoxetine, can affect estrogen signaling, though the exact mechanisms are complex and effects may be inconsistent.

Some antiepileptic drugs (AEDs) can induce liver enzymes that increase the metabolism of oral contraceptive hormones, potentially reducing their effectiveness.

Herbal supplements are not FDA-regulated, and their safety, potency, and long-term effects on estrogen levels are often not well-established. It is not recommended to use them without consulting a healthcare provider.

For women with a uterus, combining progestin with estrogen in HRT is necessary to prevent the estrogen from causing an overgrowth of the uterine lining, which can lead to cancer.