What Causes Heavy Periods? Common Reasons Your Period Is So Heavy

You're soaking through pads faster than you can change them, passing clots, and quietly wondering whether this is normal. If your periods feel heavier than they should, you're not imagining it, and you're far from alone. About 1 in 5 women experiences heavy menstrual bleeding, which adds up to more than 10 million American women each year.

Heavy periods almost always have a real, identifiable reason behind them, and many of those reasons are treatable. Here's what most commonly causes heavy menstrual bleeding, how doctors define it, and the signs that mean it's time to get checked.

What counts as a heavy period?

The medical term for heavy periods is menorrhagia, or heavy menstrual bleeding. It isn't about one slightly heavier month. Clinicians look for a consistent pattern of bleeding that's significant enough to disrupt your physical, emotional, social, or daily life.

A few practical signs suggest your bleeding may be in the heavy range:

• Soaking through one or more pads or tampons every hour for several hours in a row
• Passing blood clots larger than a quarter
• Periods that last longer than 7 days
• Needing to double up on protection or change products overnight
• Bleeding that limits your work, exercise, or social plans

Hormone imbalances and ovulation problems

The most common non-structural cause of heavy periods is a hormone imbalance, specifically between estrogen and progesterone. When your ovaries don't release an egg in a given cycle (anovulation), your body doesn't produce enough progesterone to balance estrogen. Without that balance, the uterine lining (the endometrium) keeps thickening, then eventually sheds as a heavy, sometimes prolonged period.

Several conditions drive this imbalance. Polycystic ovary syndrome (PCOS), thyroid problems like hypothyroidism, obesity, and insulin resistance can all interfere with regular ovulation. Hormone-related heavy bleeding is also especially common during puberty and perimenopause, the years approaching menopause, when cycles are naturally more irregular.

Fibroids, polyps, and other growths in the uterus

Structural problems inside the uterus are another major cause. Uterine fibroids (leiomyomata) are the most common structural reason for heavy menstrual bleeding. These are noncancerous growths in the wall of the uterus, and among people who have them, they cause heavy bleeding in roughly 30% of cases. Researchers think fibroids increase bleeding by enlarging the uterine cavity surface, interfering with how the uterus contracts, and congesting nearby blood vessels.

Other structural causes include uterine or endometrial polyps, small growths on the uterine lining, and adenomyosis, where endometrial tissue grows into the muscular wall of the uterus. Less commonly, heavy or prolonged bleeding can be an early warning sign of endometrial (uterine) cancer, which is one reason new heavy bleeding always deserves a medical evaluation.

Bleeding disorders, medications, and IUDs

Sometimes the issue isn't the uterus at all, but how your blood clots. Inherited bleeding disorders, such as von Willebrand disease, hemophilia, and platelet disorders, are an under-recognized cause of heavy periods. They're worth taking seriously: ACOG recommends that adolescents with heavy menstrual bleeding be screened for bleeding disorders and anemia, including a serum ferritin level.

Medications and devices can contribute too. Blood thinners (anticoagulants) and aspirin can increase menstrual blood loss. The copper IUD, a non-hormonal form of birth control, can also make periods heavier, especially during the first year of use. Other causes include endometriosis, pelvic inflammatory disease, pregnancy complications, and, in some cases, no identifiable cause at all.

Why heavy periods are worth treating

Beyond the disruption to daily life, heavy bleeding can quietly cost you. Losing a lot of blood month after month raises your risk of iron-deficiency anemia, which can leave you tired, lightheaded, short of breath, or pale. Untreated heavy bleeding is also linked to pain, reduced quality of life, and in more serious cases, hospitalizations or transfusions.

The encouraging news is that most causes of heavy periods can be diagnosed and managed, whether that means treating a thyroid problem, addressing fibroids, adjusting a medication, or screening for a bleeding disorder. You don't have to simply tolerate it.

When to see a doctor

It's worth talking to a clinician any time your periods regularly interfere with your life, or if you notice a clear change in how heavy or long they've become. Specific signs that warrant evaluation include soaking through a pad or tampon every hour for several hours, passing clots larger than a quarter, bleeding longer than 7 days, or symptoms of anemia like fatigue and shortness of breath.

Seek urgent or emergency care for very heavy bleeding that won't slow down, severe dizziness or fainting, or any bleeding that feels frightening. New heavy bleeding after menopause should always be checked promptly. A clinician can pinpoint the cause and build a plan that fits you. If you'd like a convenient starting point, Nolla can help you connect with clinician-overseen care to figure out next steps.