Why is My Period so Heavy with Large Clots?
Medically reviewed by Andre Stone | MD, University of Pittsburgh School of Medicine on August 25th, 2026.
Heavy periods with large clots may be a sign of heavy menstrual bleeding. Healthcare providers consider the amount and duration of bleeding, how often menstrual products must be changed, and how much the bleeding disrupts daily life; an exact blood-volume cutoff is not usually needed. Common causes include hormonal imbalances, uterine fibroids, endometriosis, polyps, or blood clotting disorders. Thyroid dysfunction and certain medications can also contribute to heavy flow. The large clots form when blood pools in the uterus before being expelled, allowing natural anticoagulants to become overwhelmed. If you're soaking through a pad or tampon every hour for several hours, contact a healthcare provider promptly. Seek urgent medical care if the bleeding is accompanied by fainting, severe dizziness, shortness of breath, chest pain, severe pelvic pain, or possible pregnancy. Repeated large clots or heavy bleeding that disrupts daily life also warrants medical evaluation.
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