Prolonged menstrual bleeding may be a side effect of certain medications or caused by hormonal fluctuations.

No two menstrual periods are exactly the same. Some last one day, while others last a week. The time between periods can also vary.

Your overall menstrual cycle can range in length from around 21 days to as long as 35 days. Cycles shorter than 21 days typically signal that ovulation may have occurred earlier than normal or not at all.

Cycles longer than 35 days indicate that ovulation isn’t occurring or it’s occurring irregularly. A period that’s longer than 7 days can also signal that ovulation hasn’t occurred.

1. Certain nonhormonal medications

Anticoagulants, such as aspirin, help prevent blood clots by prohibiting platelets from clumping together. Taken regularly, the medication can inadvertently prolong menstruation or cause heavier bleeding.

Antidepressants and epilepsy medication can also interfere with periods, causing them to be irregular, longer, or shorter. Some antidepressants can also cause heavier bleeding and painful cramps. With these medications, changes to your menstrual cycle should stop after a few months.

If any of these medications interfere for longer than 3 months, or if you’re concerned by the extent to which they’re affecting your cycle, ask a medical professional.

2. Birth control

While many forms of hormonal birth control reportedly cause lighter periods or shorter cycles, the shot may cause prolonged menstrual bleeding. The copper IUD may also cause longer or heavier periods.

If you recently switched to a new form of birth control and you’re worried about the effect it’s having on your cycle, talk with the doctor who prescribed it.

3. Emergency contraception pills

Emergency contraception pills prevent pregnancy by delaying ovulation. This can disrupt the length of your menstrual cycle, causing irregularities in your next period.

Your period might be longer, heavier, lighter, earlier, or later than usual. These symptoms should only disrupt the first period after taking the medication. Should they persist, seek out a doctor.

4. Abortion

Your first period after an abortion may be longer or shorter than expected due to your fluctuating hormone levels. You might also experience delayed menstruation.

Talk with a healthcare professional if you have any concerns about your symptoms or are experiencing severe pain.

5. Early miscarriage

An early miscarriage can happen before you even know you’re pregnant. The most common symptoms are cramping and bleeding, mimicking what would look like a heavy period.

Other symptoms include:

  • passing large blood clots or tissue
  • pain on one side of your abdomen
  • pain in your shoulder
  • diarrhea
  • vomiting

If you think you’re having a miscarriage, seek immediate medical care.

6. Uterine polyps or fibroids

Uterine polyps occur when the cells that line the uterus overgrow, resulting in a lump of tissue attached to the uterine wall. Fibroids, similarly, are growths of fibrous tissue and muscle that develop in the uterine wall.

Both fibroids and polyps can cause heavy periods that are full of clots and last longer than a week.

Fibroids can also cause:

  • abdominal distention (enlargement)
  • feeling full in your abdomen
  • difficult or frequent urination
  • pain during penetrative sex
  • low back pain
  • constipation
  • changes in vaginal discharge

If you suspect fibroids or polyps, make an appointment with a healthcare professional. They may perform a pelvic exam or recommend imaging tests to look inside the uterus.

7. Hypothyroidism

Hypothyroidism (underactive thyroid gland) occurs when the body produces too little thyroid hormone. This can cause a variety of menstrual symptoms, including periods that are heavier, longer, or more frequent than usual.

Other symptoms include:

  • fatigue
  • constipation
  • dry skin
  • unexplained weight gain
  • hoarseness
  • muscle pain or weakness
  • thinning hair

If you suspect hypothyroidism, make an appointment with a healthcare professional. They’ll likely recommend a series of blood tests to assess your levels of thyroid-stimulating hormone (TSH), thyroid hormone T-4, and thyroid hormone T-3.

8. Polycystic ovary syndrome (PCOS)

PCOS is a hormonal disorder that’s often characterized by menstrual irregularities. You might experience longer menstrual periods with heavier menstrual bleeding or infrequent menstruation.

Other symptoms include:

If you suspect PCOS, make an appointment with a healthcare professional. They may recommend blood tests to check your hormone levels or a pelvic ultrasound to look at your ovaries and uterus.

9. Endometriosis

Endometriosis occurs when uterine-like tissue grows outside of the uterus. This can cause painful menstrual periods that are heavier or longer than expected.

Other symptoms include:

  • back pain
  • pain during penetrative sex
  • spotting between menstrual periods
  • painful bowel movements

If you suspect endometriosis, make an appointment with a healthcare professional. They may perform a pelvic exam or recommend imaging tests to examine the inside of the pelvis.

10. Adenomyosis

Adenomyosis occurs when the tissue that lines the uterus begins to grow into the muscular uterine wall. This can cause painful menstrual periods that are heavier or longer than expected.

Other symptoms include chronic pelvic pain and pain during penetrative sex.

If you suspect endometriosis, make an appointment with a healthcare professional. They may perform a pelvic exam or recommend imaging tests to examine the inside of the uterus.

11. Perimenopause

You reach menopause after you experience 12 consecutive months without a menstrual period. The time before this stage is known as perimenopause. Perimenopause typically begins in your late 40s.

Menstrual irregularities are expected during this time. In addition to longer periods or heavier bleeding, you might begin to miss periods or experience lighter-than-usual bleeding.

Other symptoms include:

If you think you’re in perimenopause, consult with a healthcare professional. They can perform a blood test to make or confirm a diagnosis. They can also prescribe medication to help manage your symptoms during this transition.

12. Von Willebrand disease

This rare disorder results from low levels of von Willebrand factor, a protein that helps blood clot, or from the protein not performing as it should.

You might experience long, heavy periods or pass blood clots larger than one inch in diameter.

Other symptoms include:

  • anemia
  • excessive bleeding after an injury
  • nosebleeds that won’t stop
  • blood in your urine or stool
  • easy bruising

If you have a family history of the condition or suspect that you have a bleeding disorder, consult with a healthcare professional. They can perform blood tests to make or confirm a diagnosis.

13. Hemophilia

This rare disorder usually results from low levels of factor VIII or IX, which are proteins that help blood clot. You might experience long, heavy periods or pass blood clots larger than one inch in diameter.

Other symptoms include:

  • large bruising after minor injuries
  • unusual or excessive bleeding after an injury
  • spontaneous or unexplained bleeding
  • joint pain

If you have a family history of the condition or suspect that you have a bleeding disorder, consult with a healthcare professional. They can perform blood tests to make or confirm a diagnosis.

14. Gynecological cancer

In some cases, heavy or prolonged menstrual bleeding may be a sign of uterine, cervical, or ovarian cancer.

Other symptoms include:

  • bleeding between menstrual periods
  • unusual vaginal discharge
  • abdominal pain or cramping
  • pelvic pain or pressure
  • abdominal distention (enlargement)

If you experience these symptoms more often than not or are otherwise concerned about your risk of cancer, consult with a healthcare professional.

They can help identify the root cause of your symptoms and advise you on any next steps.

There are countless reasons for an unexpectedly long menstrual period, and many will resolve on their own without treatment.

If your symptoms aren’t particularly severe or troublesome, you might consider tracking your period for the next month or two to see if your cycle returns to your expected baseline.

But if your symptoms interfere with your daily life or you suspect a more serious underlying cause, it’s important to consult with a healthcare professional about your concerns.

Jen Anderson is a wellness contributor at Healthline. She writes and edits for various lifestyle and beauty publications, with bylines at Refinery29, Byrdie, MyDomaine, and bareMinerals. When not typing away, you can find Jen practicing yoga, diffusing essential oils, watching Food Network, or guzzling a cup of coffee. You can follow her NYC adventures on Twitter and Instagram.