SLOT: Full Definition
What are heavy periods?
Heavy periods — medically called menorrhagia or heavy menstrual bleeding (HMB) — are menstrual periods with excessive blood loss, prolonged bleeding (more than seven days), or both. Practical signs that bleeding is heavy include soaking through a pad or tampon every hour for several consecutive hours, needing double protection (pad plus tampon), passing blood clots larger than a quarter, bleeding through to clothing or bedding, and needing to change protection overnight.
Many women normalize heavy bleeding because they've always had it, or because their mothers and sisters did. We don't. Heavy bleeding produces iron deficiency, fatigue, and quality-of-life impact that doesn't have to be tolerated — and it's often a clue to a treatable underlying cause. At Modern Thyroid Clinic, we evaluate heavy periods as both a symptom worth treating and a window into hormonal and structural health.
What hormonal conditions cause heavy periods?
The most common drivers in women are:
- Hypothyroidism and Hashimotos Thyroiditis — Low thyroid hormone disrupts platelet function, alters estrogen metabolism, and commonly produces heavier, longer cycles. Often missed when TSH alone is checked.
- Perimenopause — Anovulatory cycles produce unopposed estrogen and a thicker uterine lining; periods often become heavier and more erratic in the 40s.
- Estrogen Dominance — Relative excess of estrogen vs. progesterone thickens the lining and produces heavier flow.
- Uterine fibroids and adenomyosis — Common structural causes; should be assessed with pelvic ultrasound.
- Endometriosis — Often produces heavy, painful periods.
- Polyps — Endometrial or cervical polyps can cause heavy bleeding.
- Bleeding disorders — Von Willebrand disease and platelet dysfunction; often present from menarche.
- IUDs (copper) — Commonly increase flow.
- Polycystic Ovary Syndrome — Less commonly heavy, but anovulatory cycles can produce heavy episodes.
When is it a red flag?
Seek prompt evaluation for soaking through a pad or tampon every hour for more than two hours, passing very large clots, bleeding lasting more than 10 days, severe pelvic pain, lightheadedness or fainting, or signs of significant anemia (severe fatigue, shortness of breath, racing heart). Bleeding after menopause is always abnormal and warrants prompt evaluation. Heavy bleeding accompanied by easy bruising or bleeding from gums may suggest a bleeding disorder.
What typically helps
At Modern Thyroid Clinic, heavy periods prompt a thorough workup: a complete thyroid panel (TSH, Free T4, Free T3, antibodies), full iron studies including Ferritin, CBC, FSH and estradiol where perimenopause is suspected, and pelvic ultrasound to evaluate the uterus and ovaries. Bleeding disorder workup is added when history suggests it. Treatment depends on cause:
- Thyroid disease — Optimizing thyroid hormone often resolves heavy bleeding within a few cycles.
- Perimenopause and estrogen dominance — Bioidentical Progesterone Bioidentical in the luteal phase often dramatically reduces flow.
- Fibroids and adenomyosis — May require gynecology consultation; options range from medical management to procedures.
- Iron repletion — Almost always needed; we treat aggressively because heavy bleeders are commonly iron-deficient even before they're frankly anemic.
Many women see meaningful improvement within three to six months once the underlying driver is identified and addressed.
Common symptoms
Common questions
How do I know if my periods are actually heavy?
Practical thresholds: soaking through a pad or tampon every hour for several consecutive hours, needing double protection, passing clots larger than a quarter, bleeding more than seven days, bleeding through to clothing or bedding, or needing to change protection overnight. If your period limits where you go, what you wear, or what you do — that's heavy. The Pictorial Blood Loss Assessment Chart and the FIGO criteria are formal tools, but the simpler test is impact on your life and your iron stores.
Can my thyroid really make my periods heavier?
Yes — and it's one of the most underrecognized causes of heavy bleeding. Hypothyroidism affects platelet function, slows estrogen clearance, and commonly produces heavier, longer cycles. Many women with persistent heavy bleeding have undiagnosed Hashimoto's, including women whose TSH is technically 'normal' but whose Free T3 is low or whose antibodies are elevated. A complete thyroid panel — not just TSH — is essential when periods are heavy. Treating the thyroid often resolves the bleeding within a few cycles.
Why does my doctor want to check my iron?
Heavy menstrual bleeding is the leading cause of iron deficiency in women of reproductive age. Iron deficiency can cause significant fatigue, brain fog, hair loss, restless legs, and brittle nails — long before hemoglobin drops out of the 'normal' range and a doctor calls you anemic. At Modern Thyroid Clinic we look at full iron panels including [ferritin], and we treat ferritin under 50-70 ng/mL even with 'normal' hemoglobin because that range matches how women actually feel. Iron repletion alongside addressing the bleeding cause is essential.
Think you might be dealing with this?
Talk to a Modern Thyroid Clinic specialist about your symptoms, labs, and next steps.
Book a Discovery CallThis content is for educational purposes only and is not medical advice. Consult a licensed clinician for diagnosis and treatment. Content on this page does not create a doctor-patient relationship with Modern Thyroid Clinic.