6 reasons for sudden heavy periods

Qualified Nutritionist (BSc, MSc, RNutr)
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12 May 2022

What counts as a heavy period?

Before I start to explain the reasons why periods can suddenly get heavier, I thought it would be useful to examine what defines a period as heavy in the first place

Firing through the box of tampons or pads

The first thing to consider is the amount of sanitary products you have to use during the course of your period. If you have to change your sanitary pad or tampon every hour or two then this can definitely not be considered normal. Also, if you find yourself having to use more than one of these products (known as 'double protection') at the same time in order to protect yourself from leakages then again, this can be deemed a heavy period. 

Lots of leakages

If leakages, known as flooding, are a common occurrence for you then this may also indicate that your period is heavy and can be associated with clots. However, do bear in mind that the strength of your chosen sanitary product may just be inadequate for your flow.

A long period

Another thing to consider here is the length of your period. It is normal for periods to last anywhere between three and seven days but if yours lasts beyond this it’s an indicator that things are a little heavier than they should be.

Large blood clots

Most women pass blood clots during the course of their periods so the key here is the size. If yours are regularly bigger than a 10 pence piece then it suggests your period is overly heavy.

Signs of anaemia

Anaemia occurs when your blood lacks red blood cells or haemoglobin and so it often comes about as a direct result heavy periods. It can cause symptoms such as fatigue, shortness of breath, heart palpitations and pale skin so is definitely something to look out for if you think your periods are heavy.

Lots of blood

Many women are preoccupied with how much blood they are losing each month and although this can indicate whether or not your period is heavy, the factors above must be considered as well. 

As a rule though, most women lose less that 16 teaspoons of blood during the course of their periods and the average is 6 to 8 teaspoons. A heavy period is anything more than this but, as we don’t measure the amount of blood coming out, this isn’t the most accurate way to determine if your period is heavy or not. With experience though, most women can tell what a normal period is and what is not. 

Reasons for heavy periods

Now you know what is classed as a heavy period, let's take a look at 6 reasons which could be causing you to experience heavy periods:

1. Changes to weight

As I discussed extensively in my blog ‘Could your weight be affecting your periods?’, gaining weight can influence how heavy your period is. This is partly because fat cells hold oestrogen which they then release into the rest of our body. This can result in oestrogen dominance, a problem that is characterised by heavy periods, painful breasts, bloating, irritability and mood swings. 

Losing lots of weight on the other hand, can lead to a shortage of oestrogen and as a result symptoms such as low mood and light, infrequent periods can become problematic.

2. New medications

Medications come with all sorts of side effects but sometimes they can even make your period heavier. I’ve listed a few common culprits below.


Although this has a number of uses, aspirin is most commonly used for pain relief. In fact, many women call upon it to ease their period cramps however, aspirin has blood thinning properties which can contribute to heavier periods.  


These medications are used to prevent blood clots but, you’ve guessed it, they can also result in heaver periods.

3. Changes to your birth control

I have written about methods of contraception in previous blogs but here I focus on how changing birth control methods can affect the amount you bleed. 

Contraceptive patch and the pill

These contraceptives usually result in a lighter flow so if you’ve recently stopped using either of them you may experience a heavier period.

The non-hormonal coil

This common contraceptive is non-hormonal and commonly referred to as the 'copper coil.' It is inserted in the uterus by a doctor or nurse to stop you getting pregnant. Although it is very effective and can last for years, it comes with the unfortunate side effect of heavier and more painful periods. 

Nevertheless, this is only temporary problem and things should settle down after a few period cycles. After all, the body needs time to adjust to the new hormone balance that contraceptives bring.

There is an alternative, hormonal coil known as the Mirena coil which can offer some hormonal support, and in some cases, make periods much lighter, shorter, or can even cause them to disappear completely.

4. An underlying condition

If you are experiencing heavy periods it’s important that you don’t try to self-diagnose. Instead a trip to your doctor will confirm or exclude any of the issues below.

Dysfunctional uterine bleeding (DUB) 

This common condition comes about as a result of an imbalance in hormone levels. It can cause bleeding to occur outside the usual period of menstruation, as well as heavy bleeding. It can happen at any time of a woman’s reproductive years but is most common after the age of 40. 

Uterine fibroids 

These are non-cancerous growths that develop in or around the uterus. It is unclear exactly why these growths develop though it may be linked to drop in oestrogen levels. It is common amongst fertile women and causes, amongst other things, pain, constipation and heavy periods.

Underactive thyroid

This condition occurs when the thyroid does not produce enough hormones causing symptoms such as weight gain, tiredness and feelings of depression. However, the condition is also associated with more painful and heavier periods.


This occurs when the lining of the uterus becomes embedded in the wall of the womb. It causes painful periods as well as a much heavier flow.

5. PMS

Premenstrual syndrome is characterized by a range of symptoms including heavy periods, irritability, fluid retention and painful periods. Unfortunately the exact cause of PMS is unclear though it is probably to do with an imbalance in the ratio of progesterone and oestrogen in the body. Also, things like diet and stress are known to worsen symptoms. 

6. Menopause

Hormone levels fluctuate as you approach the menopause and this, perhaps a little surprisingly, can also contribute to heavier periods. Heavy cycles are more likely to develop just before the menopause when the body eases out of reproductive mode and oestrogen levels peak. This is usually accompanied by irregular periods and feelings of exhaustion.

If you’d like some more information on the menopause then our expert Eileen has a multitude of blogs on the subject. Click the link to find her most recent ones. 

How to treat the problem?

If you have one heavy period, it can be common to experience these infrequently and there may be no need to consult your GP. However, if you experience a persistent change with a heavier flow for three months or more, you should consult your doctor. Also, the NHS state that if you are experiencing other symptoms such as severe cramp and bleeding between periods then a doctor will be able to see if there is an underlying cause for this.

Some common treatments for heavy periods include contraceptives though I won't go into the details much more than this as what you are prescribed will depend on what's going on with your body!

Once you've got the green light from your doctor, a herbal remedy such as Agnus castus may be used to address heavy periods. 

This symptom is often associated with too much oestrogen or too little progesterone but the remedy helps to balance these things out. Please note however, that Agnus castus cannot be used alongside hormonal contraceptives.

Agnus castus | Helps Relieve Pre-Menstrual Symptoms | Mood Swings, Menstrual Cramps, Bloating & Breast Tenderness

£11.99 (50ml)

Originally published in September 2018, updated and reviewed in May 2022.

Agnus castus | Helps Relieve Pre-Menstrual Symptoms | Mood Swings, Menstrual Cramps, Bloating & Breast Tenderness


£ 11.99

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A traditional herbal remedy used to relieve the symptoms of PMS
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