If you’re wondering what causes heavy periods in women, there are several possible explanations, ranging from hormonal changes to conditions such as fibroids, endometriosis, adenomyosis, and thyroid problems. Heavy periods can affect everyday life and, in some cases, contribute to iron-deficiency anaemia.
An occasional heavier period does not necessarily mean something is wrong. However, if your periods suddenly become much heavier, last longer than usual, or interfere with your normal activities, it is worth speaking to your GP.
Understanding what causes heavy periods in women can help you recognise when menstrual changes need further investigation.
What Is Considered a Heavy Period?
How do I know if my period is too heavy?
Heavy menstrual bleeding is sometimes called menorrhagia. Rather than trying to measure an exact amount of blood loss at home, it can be more useful to consider how your bleeding affects your daily life.
Possible signs include:
- Needing to change period products very frequently
- Needing to use two types of period products together
- Bleeding through clothes or bedding
- Periods lasting longer than usual
- Passing large blood clots
- Avoiding normal activities because of bleeding
- Feeling unusually tired or short of breath
If these problems regularly occur during your period, discuss them with your GP. Looking after your menstrual health is also important, and understanding the common mistakes to avoid during the menstruation phase may help you manage your cycle more comfortably.
What Causes Heavy Periods in Women?
Why are my periods suddenly so heavy?
There is no single answer to what causes heavy periods in women. Menstrual bleeding is influenced by hormones and the health of the uterus, so several different conditions can change the amount or duration of bleeding.
Here are some common possibilities.
1. Hormonal Changes
Can hormonal imbalance cause heavy periods?
Yes. Changes in the hormones that regulate ovulation and the menstrual cycle can sometimes cause the lining of the uterus to build up differently, resulting in heavier or unpredictable bleeding.
Hormonal changes may occur during puberty, perimenopause, or alongside certain medical conditions.
2. Uterine Fibroids
Can fibroids cause heavy periods?
Yes. Fibroids are non-cancerous growths that develop in or around the womb and are a common cause of heavy menstrual bleeding.
Other possible symptoms include:
- Pelvic pressure
- Abdominal discomfort
- Frequent urination
- Lower back pain
- Pain during sex
Some women with fibroids have no symptoms at all.
3. Endometriosis
Can endometriosis cause heavy periods?
Endometriosis can be associated with heavy periods, although pain is often one of its most prominent symptoms.
You may also experience:
- Severe period pain
- Pelvic pain
- Pain during or after sex
- Pain when passing urine or opening your bowels during your period
- Difficulty becoming pregnant
Persistent symptoms should be assessed by a healthcare professional.
4. Adenomyosis
What is adenomyosis, and can it cause heavy bleeding?
Adenomyosis occurs when tissue similar to the womb lining grows into the muscular wall of the uterus.
It can cause:
- Heavy periods
- Painful periods
- Pelvic pain
- A feeling of heaviness or fullness in the abdomen
Symptoms vary considerably between women.
5. Polycystic Ovary Syndrome (PCOS)
Can PCOS cause heavy periods?
PCOS commonly causes irregular or infrequent periods because ovulation may not occur regularly.
When a period eventually happens after a longer gap, some women may experience heavier bleeding.
Other signs of PCOS can include acne, excess facial or body hair, and difficulties becoming pregnant.
6. Perimenopause
Can perimenopause make periods heavier?
Yes. During perimenopause, hormone levels fluctuate as the body gradually approaches menopause.
Your periods may become:
- Heavier
- Lighter
- Longer
- Shorter
- More or less frequent
Although menstrual changes are common during perimenopause, unusually heavy or persistent bleeding should still be discussed with your GP.
7. Thyroid Problems
Can thyroid problems cause heavy periods?
An underactive thyroid can sometimes be associated with heavy or irregular menstrual bleeding.
Other symptoms may include fatigue, weight changes, feeling unusually cold, dry skin, or difficulty concentrating.
Because these symptoms have many possible causes, proper medical assessment is important.
8. Certain Medicines and Contraception
Can medication cause heavier periods?
Yes. Certain medicines can affect menstrual bleeding.
Some types of contraception may also alter your periods. For example, a copper intrauterine device (IUD) can make periods heavier or more painful, particularly after insertion.
Never stop prescribed medication without speaking to your healthcare professional.
9. Bleeding Disorders
Can a bleeding disorder cause heavy periods?
Yes. In some women, very heavy periods may be related to an underlying bleeding disorder.
This possibility may be considered particularly when heavy periods have been present from a young age or there is also frequent bruising, prolonged bleeding, or a family history of bleeding problems.
10. Other Gynaecological Conditions
Can heavy bleeding be a sign of something more serious?
Sometimes.
Polyps and other conditions affecting the womb or cervix can cause abnormal bleeding. Less commonly, abnormal bleeding can be associated with cancer of the womb or cervix.
This does not mean that heavy periods usually indicate cancer. However, unexplained changes should be properly investigated rather than self-diagnosed.
Could Heavy Bleeding Be Related to Pregnancy?
Can you have period-like bleeding when pregnant?
Bleeding during pregnancy is not considered a menstrual period. If pregnancy is possible and you are experiencing unusual or heavy bleeding, it is important not to assume that it is simply your normal period. You can learn more about whether women can still have a period when pregnant.
Bleeding in early pregnancy can have different causes. If you are pregnant and bleeding, particularly if the bleeding is heavy or accompanied by pain, seek appropriate medical advice.
If miscarriage is a concern, our guide explains how long a miscarriage may take once bleeding starts. You can also read about things that can cause a miscarriage in the first 8 weeks for further information about early pregnancy loss.
Can Heavy Periods Cause Anaemia?
Why do I feel exhausted during my period?
Repeated heavy menstrual bleeding can lead to iron-deficiency anaemia because the body loses iron through blood.
Possible symptoms include:
- Tiredness
- Weakness
- Shortness of breath
- Headaches
- Dizziness
- Heart palpitations
- Pale skin
Your GP may recommend a blood test if anaemia is suspected.
When Should I Worry About Heavy Periods?
When should I see a GP about heavy periods?
Arrange an appointment if your periods have become noticeably heavier, regularly interfere with everyday activities, last longer than expected, or are accompanied by significant pain.
You should also seek medical advice for:
- Bleeding between periods
- Bleeding after sex
- Bleeding after menopause
- Persistent pelvic pain
- Severe tiredness or breathlessness
- A significant unexplained change in your normal menstrual pattern
Seek urgent medical attention if bleeding is extremely heavy and you feel faint, very weak, severely unwell, or otherwise concerned about your immediate health.
How Are Heavy Periods Diagnosed?
What tests might be needed for heavy periods?
Your GP will usually start by discussing your menstrual cycle, symptoms, medical history, contraception, and medications.
Depending on your circumstances, further assessment may include:
- Blood tests
- Pregnancy testing where relevant
- Pelvic examination
- Ultrasound
- Other specialist investigations
The tests recommended will depend on your age, symptoms, medical history, and suspected cause.
How Are Heavy Periods Treated?
Can heavy periods be treated?
Yes. Treatment depends on what causes heavy periods in women and how severely the bleeding affects daily life.
Options may include medicines that reduce bleeding, hormonal contraception, treatment for iron-deficiency anaemia, or treatment of an underlying condition such as fibroids or adenomyosis.
Some women may require specialist procedures or surgery when other treatments are unsuitable or ineffective.
Frequently Asked Questions
What is the most common cause of heavy periods?
There are many possible causes, including hormonal changes, fibroids, adenomyosis, contraception, and other gynaecological conditions. The cause cannot always be identified from symptoms alone.
Can stress cause heavy periods?
Stress can affect the menstrual cycle, but persistent heavy bleeding should not automatically be attributed to stress. Speak with your GP if the change continues.
Are heavy periods normal during perimenopause?
Periods can become heavier or more irregular during perimenopause. However, significant or persistent changes should still be assessed.
Can heavy periods affect fertility?
Heavy bleeding itself does not necessarily cause infertility, but some underlying causes, including fibroids and endometriosis, may affect fertility in some women.
Should I see a gynaecologist for heavy periods?
Your GP is usually a good first point of contact in the UK. If specialist investigation or treatment is required, you may be referred to a gynaecologist.
Final Thoughts
Understanding what causes heavy periods in women is important because heavy menstrual bleeding is not something you simply have to tolerate.
Hormonal changes, fibroids, adenomyosis, endometriosis, PCOS, thyroid conditions, medicines, and other health problems can all contribute to heavier bleeding.
If your periods are disrupting everyday life or have changed significantly from what is normal for you, speak with your GP. Identifying the underlying cause can help you access appropriate treatment and protect your long-term health.
Medical Disclaimer
This article is for general educational purposes only and does not replace professional medical advice, diagnosis, or treatment. If you experience persistent heavy periods, abnormal bleeding, severe pain, dizziness, fainting, or other concerning symptoms, seek advice from a qualified healthcare professional.
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