Heavy Periods (Menorrhagia): Causes, Signs and When to See a Doctor
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Changing your protection almost every hour, getting up at night to change, cancelling plans during your period? Heavy periods (or menorrhagia) are very common, but you don't have to put up with them in silence. Here are the possible causes, the signs that mean you should see a doctor and the treatments available, backed by reliable sources.
In short
- Menorrhagia means losing 80 ml of blood or more per cycle, according to the SOGC. But what matters most is how it affects your life.
- Possible causes: hormones, bleeding disorders, fibroids or polyps, medications. In up to half of cases, no specific cause is found.
- See a doctor if your period lasts more than 7 days, if you soak through a product every hour for several hours, or if you often feel tired and short of breath.
- Effective treatments exist, and not all of them are hormonal.
Heavy periods or menorrhagia: what are we talking about?
According to the Society of Obstetricians and Gynaecologists of Canada (SOGC), menorrhagia is clinically defined as a loss of 80 ml of blood or more in one cycle. The Government of Canada's Guide to Menstrual Health puts a typical period at about 30 to 80 ml of blood, over three to eight days.
Nobody measures their blood down to the millilitre, and the SOGC says so itself: your perception of your bleeding matters more than the actual amount lost. If your period keeps you from work, school or your activities, that's reason enough to talk about it. And you're not alone: according to the American College of Obstetricians and Gynecologists (ACOG), about one third of women seek treatment for heavy periods. For the basics, also read Menstrual flow: how much blood do you lose?
Signs of heavy periods
According to the SOGC, heavy menstrual bleeding shows up as:
- periods lasting more than 7 days;
- bleeding that soaks through a tampon or pad every hour for several hours in a row;
- needing to wear more than one product at a time;
- needing to change during the night;
- blood clots the size of a quarter or larger.
The NHS, the UK's public health service, adds two more signs: avoiding activities or taking time off work because of your period, and often feeling tired or short of breath.
What causes heavy periods?
The SOGC groups the causes into four main categories.
1. Hormonal causes
According to the Merck Manual, ovulation problems can cause abnormal bleeding. They can be linked to polycystic ovary syndrome (PCOS), the thyroid, extreme stress or the hormonal changes of puberty and perimenopause. The Government of Canada notes that heavy periods are common during perimenopause.
2. Bleeding disorders
According to the SOGC, von Willebrand disease affects 1 to 2% of the population, and heavy periods are its most common symptom in women. It's often discovered while looking into why first periods are so heavy. If your periods have been very heavy from the start, talk to your doctor.
3. Changes in the uterus
Fibroids, polyps and adenomyosis are causes described by the Merck Manual and the NHS, as is endometriosis. Good news: according to the Government of Canada, polyps and fibroids are typically not harmful, and cancers of the uterus are rare.
4. Medications
The NHS lists some anticoagulants and chemotherapy medicines, and ACOG adds aspirin and the copper IUD. Never stop a medication without talking to your doctor or pharmacist.
And sometimes, no cause at all. According to the SOGC, in up to half of cases the cause can't be identified. That doesn't mean you have to live with it: treatments still exist.
When should you see a doctor for heavy periods?
| Your situation | What to do |
|---|---|
| One of the signs above, or periods that disrupt your daily life | Book an appointment with your family doctor, a nurse practitioner or a clinic. |
| Bleeding between periods, after sex or after menopause | See a doctor promptly. |
| Fatigue, weakness, dizziness or shortness of breath | See a doctor: these can be signs of anemia. |
| Severe pain during your period | Talk to your doctor. |
| Not sure if it's urgent | Call 811 (Info-Santé in Quebec). |
What happens at the doctor's
According to the Merck Manual, the most common tests are a pregnancy test, a complete blood count (to check for anemia), blood clotting tests, hormone levels and a pelvic ultrasound. An endometrial biopsy or a hysteroscopy is sometimes suggested.
To prepare for your appointment, track for two or three cycles how long your period lasts, how many products you use per day, whether you wake up at night, any clots, your fatigue, your medications and any bleeding problems in your family (some bleeding disorders are inherited).
Possible treatments
According to the Government of Canada and the NHS, not everyone needs treatment: it's a decision to make with your doctor, based on your symptoms and your plans. The main options:
- Non-hormonal: tranexamic acid, taken during your period to reduce bleeding (SOGC, NHS), or certain prescription anti-inflammatories such as mefenamic acid or naproxen (NHS).
- Hormonal: hormonal IUD, pill, patch, ring, implant or injection. According to the Government of Canada, using them to reduce or stop periods does not impact future fertility.
- Treating the cause: a bleeding disorder (ACOG) or anemia.
- Procedures, less often: endometrial ablation, fibroid removal or hysterectomy (NHS).
Heavy periods and iron: watch out for anemia
According to the Government of Canada, heavy flow can reduce your iron stores and lead to iron-deficiency anemia: fatigue, weakness, dizziness, shortness of breath, sometimes an irregular heartbeat. ACOG notes that severe anemia can increase the risk of heart problems. More iron in your diet or a supplement can help prevent it, but ask your doctor or pharmacist before taking iron.
Living with heavy periods day to day
The right protection takes a lot of stress away. Our heavy flow period underwear is designed in Quebec with a soft, breathable, odour-fighting fabric. At night, the period boxer, with more coverage, protects better when you're lying down. On your heaviest days, you can also use it as backup with a cup or a tampon. To know how often to change, read Period underwear: how long can you wear it?
Frequently asked questions
Are heavy periods dangerous?
Most of the time, the cause isn't serious. But repeated heavy periods can lead to anemia, so they're worth getting checked.
My teen has very heavy periods. Is that normal?
According to the NHS, periods can be heavier when they first start. But according to the SOGC, this is often how von Willebrand disease is discovered. When in doubt, see a doctor. Also see our guide Period underwear for teens.
Is period underwear enough with menorrhagia?
Yes, if it's designed for heavy flow and changed on time. If you soak through any product within an hour or two, it's not a protection problem: it's a sign to show your doctor.
In summary
Heavy periods have many possible causes: hormones, bleeding disorders, fibroids or polyps, medications, or sometimes no specific cause. The right reflex: track your symptoms, see a doctor if your period disrupts your life or wears you out, and keep an eye on your iron. Effective treatments exist.
References
- Society of Obstetricians and Gynaecologists of Canada (SOGC), Heavy Menstrual Bleeding (HMB) Overview (YourPeriod.ca): definition of menorrhagia (80 ml), signs, cause categories, unknown cause in up to half of cases.
- Society of Obstetricians and Gynaecologists of Canada (SOGC), Bleeding Disorders That Cause HMB: von Willebrand disease and tranexamic acid.
- Government of Canada, Guide to Menstrual Health (2026): typical periods, warning signs, iron-deficiency anemia, treatment options.
- Merck Manual Consumer Version, Abnormal Uterine Bleeding (AUB) (2026): causes and diagnostic tests.
- NHS, Heavy periods (2024): signs, when to see a doctor, causes and treatments.
- American College of Obstetricians and Gynecologists (ACOG), Heavy Menstrual Bleeding: how common it is, medication-related causes, anemia.
This article is for information only and does not replace advice from a health professional. If in doubt, see your doctor or call 811 (Info-Santé in Quebec).