Periods, irregular - Causes 

Causes of irregular periods 

Your menstrual cycle can be disturbed if you change your method of contraception or you have an imbalance of the hormones oestrogen and progesterone.

It is not unusual to have a hormone imbalance for a few years after puberty and before the menopause. This can cause your menstrual cycle to become longer or shorter. Your periods may also become lighter or heavier.

If your irregular periods are caused by these age-related factors, you will not usually need to see your GP.


The following lifestyle factors can also upset your balance of hormones and cause irregular bleeding:

  • extreme weight loss or weight gain
  • excessive exercise
  • stress


An intrauterine system (IUS) or contraceptive pill may cause spotting between periods.

An intrauterine device (IUD) doesn't cause irregular periods, but can cause heavy bleeding or painful bleeding.

Small bleeds, known as breakthrough bleeds, are common when the contraceptive pill is first used. They are usually lighter and shorter than normal periods, and usually stop within the first few months.

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) occurs when very small cysts (small, fluid-filled sacs) develop in the ovaries.

The usual symptoms of PCOS are irregular or light periods, or no periods at all. This is because, in women with PCOS, ovulation (the release of an egg) may not take place as often as normal. Also, the production of hormones may be unbalanced, and you could have higher levels of testosterone than normal (this is a male hormone that women normally have a small amount of).

Read more about polycystic ovary syndrome.

Gynaecological problems

Irregular bleeding can also be due to unsuspected pregnancy, early miscarriage or problems with the womb or ovaries. Your GP may refer you to a gynaecologist (specialist in diseases of the female reproductive system) if further investigation and treatment are needed.

Thyroid disorders

A thyroid disorder is another possible but rare cause of irregular periods (the thyroid gland, found in the neck, produces hormones that maintain the body's metabolism). Your GP may test for a thyroid problem by taking a blood test to check levels of thyroid hormones in your blood.

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Page last reviewed: 04/04/2013

Next review due: 04/04/2015


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The 3 comments posted are personal views. Any information they give has not been checked and may not be accurate.

mashego ck said on 24 July 2014

Hi guys

I have a problem with my periods, since from april when I started to ues a 2months injection my periods comes regularly but its too small, it ddnt even need a pads, n its only last for few seconds, my problem I that I want to have a baby, is there any chances I can become pregnant? I only used that injection for for 3 months now I uuse pills, cause the sister at the clinic said I should use it n it will help for my problem. Bt still not helping. Please help me I dnt no what to do anymore. Iam 32 yrs old

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Shevon Simon said on 16 November 2013

It's always wise to get some blood tests and a gynaecological examination done if we are experiencing difficulty or noticing abnormalities with our period.

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User671632 said on 30 April 2012

im 23 yrs old i started my periods when i was 13. my periods have always started on the 28th of every month, even coming off the pill. since July 2011 my periods have not been on time, i come on when ever. ive always lasted for 3days but this month i lasted 4 days. are my periods still ok ?

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Ruling out pregnancy

If you have irregular periods, your GP may recommend a pregnancy test and ultrasound scan to rule out a possible pregnancy, particularly if you are in pain (pain could mean you are having an ectopic pregnancy or miscarriage).