What Hormones Cause Fibroids To Grow and Fibroids: What to Know

What Hormones Cause Fibroids To Grow and Fibroids: What to Know

Uterine fibroids (leiomyomas) are noncancerous growths of the uterus that affect up to 70–80% of women by age 50. If you or someone you love is dealing with fibroids, you’ve likely heard that “hormones feed them.” That’s largely true—but the story is more nuanced. Understanding which hormones drive fibroid growth, how this changes across life stages, and what treatments target these pathways can help you make informed decisions.

The short answer: estrogen and progesterone are the main drivers

Research consistently shows that the ovarian hormones estrogen and progesterone stimulate fibroid growth. Fibroids contain higher levels of estrogen and progesterone receptors than normal uterine muscle, making them especially responsive to these hormones. Estrogen tends to “prime” fibroid tissue—upregulating progesterone receptors—while progesterone further promotes growth and the accumulation of extracellular matrix (the tissue scaffold that makes fibroids firm).

Evidence for this hormonal dependence includes:

  • Fibroids rarely appear before puberty and often shrink after menopause, when estrogen and progesterone decline.
  • During pregnancy, when both hormones surge, fibroids can enlarge; they often regress after delivery.
  • Medications that suppress ovarian hormone production (such as GnRH agonists or antagonists) shrink fibroids and reduce bleeding.

How hormones influence fibroids across life stages

Menstrual years

During reproductive years, monthly cycles expose fibroid tissue to fluctuating estrogen and progesterone. Estrogen in the first half of the cycle stimulates cell growth and receptor expression; progesterone in the second half can drive further growth and matrix production. This ebb and flow helps explain why symptoms—like heavy bleeding or pressure—may wax and wane.

Pregnancy and postpartum

Fibroids may grow during pregnancy due to high levels of estrogen and progesterone. Growth is most common in the first and second trimesters. Postpartum, as hormone levels fall, many fibroids stabilize or shrink. The impact on pregnancy varies; most pregnancies progress normally, but some people experience pain, bulk symptoms, or rarely complications. Always discuss your personal risks with your obstetric provider.

Perimenopause and menopause

As ovarian hormone production declines, fibroids typically stop growing and often shrink after menopause. However, symptom relief isn’t guaranteed for everyone, especially if significant bulk symptoms already exist.

Hormone therapy after menopause

Menopausal hormone therapy (HRT) can sometimes stimulate fibroid growth. If you use HRT, clinicians usually monitor fibroid-related symptoms and may adjust therapy if growth or bleeding occur.

Beyond estrogen and progesterone: other signals that matter

While estrogen and progesterone are central, several other pathways influence fibroid biology:

  • Local estrogen production: Some fibroids express aromatase, an enzyme that converts androgens into estrogen locally within the fibroid.
  • Growth factors and extracellular matrix: Insulin-like growth factor (IGF), transforming growth factor-beta (TGF-β), and other signals promote cell proliferation and the dense collagen matrix that characterizes fibroids.
  • Metabolic and lifestyle factors: Higher body mass index can increase circulating estrogen from peripheral conversion, which may contribute to risk and growth. Vitamin D deficiency has been associated with higher fibroid risk in some studies, though supplementation for treatment remains under investigation.

Birth control, HRT, and fibroid growth: what we know

  • Combined oral contraceptives (estrogen + progestin): Often reduce menstrual bleeding and cramps. Most studies suggest minimal effect on fibroid size, though they don’t typically shrink fibroids.
  • Progestin-only methods: The levonorgestrel-releasing IUD (LNG-IUD) can substantially reduce heavy bleeding due to fibroids but has limited impact on shrinkage. Data on depot medroxyprogesterone acetate (DMPA) are mixed; it may reduce bleeding and in some studies is associated with lower fibroid risk or size, but it is not a primary shrinkage therapy.
  • Menopausal hormone therapy: May promote growth in some postmenopausal patients; careful monitoring is advised.

Medications that target hormones to treat fibroids

Several FDA-approved options reduce fibroid symptoms by lowering or modulating estrogen and progesterone signaling. These are typically used to control heavy menstrual bleeding, improve anemia, and sometimes shrink fibroids before surgery.

  • GnRH agonists (e.g., leuprolide): Temporarily suppress ovarian hormone production, often shrinking fibroids and reducing bleeding. Side effects can include hot flashes, bone density loss, and mood changes; duration is usually limited, sometimes with “add-back” estrogen/progestin to mitigate side effects.
  • Oral GnRH antagonists with add-back therapy:
    • Elagolix with estradiol/norethindrone acetate (brand: Oriahnn): FDA-approved to reduce heavy menstrual bleeding due to fibroids. It directly lowers ovarian hormone production; the co-packaged add-back helps protect bone and reduce hot flashes. Use is generally limited to 24 months due to bone loss risk.
    • Relugolix combination (relugolix/estradiol/norethindrone acetate; brand: Myfembree): Also FDA-approved for heavy menstrual bleeding associated with fibroids, with similar benefits and time limitations related to bone health.
  • Tranexamic acid: A non-hormonal option taken only during menses to reduce heavy bleeding. It does not shrink fibroids.

Important safety notes: GnRH-based therapies may carry risks including bone mineral density loss and thromboembolic events when used with estrogen/progestin add-back. They are contraindicated in pregnancy and certain cardiovascular risk settings. Review FDA Medication Guides and discuss your medical history with your clinician.

When surgery or procedures are considered

When symptoms are severe, structural distortion is significant, or medical therapy isn’t sufficient, procedures may help:

  • Myomectomy (surgical removal of fibroids) preserves the uterus and fertility potential.
  • Uterine artery embolization reduces fibroid blood supply, shrinking fibroids and easing symptoms.
  • Radiofrequency ablation and MRI-guided focused ultrasound are less invasive options in selected cases.
  • Hysterectomy is definitive for people who do not desire future pregnancy.

Procedure choice depends on fibroid number, size, location, symptoms, fertility goals, and overall health.

What you can do now

  • Track symptoms: Note bleeding days, pad/tampon counts, pain, and pressure symptoms. Share this with your clinician.
  • Optimize iron and overall health: Treat anemia, maintain a balanced diet, and consider evaluation of vitamin D status with your clinician.
  • Ask targeted questions: Which options control bleeding? Which may shrink fibroids? How might treatments affect fertility or menopause timing?

Key takeaways

  • Estrogen and progesterone are the main hormones that cause fibroids to grow.
  • Fibroids often enlarge during high-hormone states (pregnancy) and shrink after menopause.
  • Birth control can control symptoms; GnRH-based medications can reduce bleeding and shrink fibroids but require monitoring.
  • Treatment is individualized—consider your symptoms, goals, and medical history.

Trusted sources and further reading

This article is for education and does not replace personalized medical advice. Talk with a qualified clinician to choose the best approach for you.

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