COVID-19 Information - To see our up to date advice for using our pharmacies - Click Here

Health Knowledge and Encyclopedia

At your local Pearn's Pharmacy we can offer advice on most general health matters. You can also use our Health Encyclopaedia to provide you with the tools and links you need to pinpoint symptoms and get a full explanation of a suspected condition.

Search By Letter
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y |

Search by Keyword

Periods, irregular


Menstruation, or periods, is the monthly shedding of the lining of the womb.

Periods are part of the female reproductive cycle. They start during puberty (between the ages of 10 and 16) and continue until the menopause (45 to 55). The average menstrual cycle lasts 28 days, but can vary between 24 and 35 days.

It can take up to two years for periods to settle into a regular cycle. After puberty, most women develop a regular menstrual cycle, with around the same length of time between periods.

Menstrual bleeding normally lasts between two and seven days, with the average being five days. 

However, some women have an irregular menstrual cycle. This is where the time between periods, the amount of blood lost and the number of days bleeding lasts all vary widely.

Why are periods sometimes irregular?

The pattern of a woman's menstrual cycle can be disturbed by a change in contraception method. It could also be affected by an imbalance of the hormones oestrogen and progesterone, which regulate the menstrual cycle. Many factors can cause a hormone imbalance (see Causes).

Irregular periods are common during puberty or nearing menopause. Treatment during these times is usually not necessary.

More information

For more information on periods, and specific information on heavy periods, absent periods and painful periods, see Selected links.

^^ Back to top


Causes of irregular periods 

The pattern of a woman's menstrual cycle can be disturbed by:

  • changing the contraception method, or
  • an imbalance of the hormones oestrogen and progesterone, which regulate the menstrual cycle.

There are several factors, outlined below, which can cause a hormone imbalance.

Polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) occurs when many 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 PCOS, ovulation (the releasing of an egg) often does not take place. Also, the production of hormones may be unbalanced, and you could have higher levels of testosterone (a male hormone that women have a small amount of) than normal.


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

  • extreme weight loss or gain,
  • heavy exercise, or
  • stress.


It is not unusual to have a hormone imbalance for a few years after puberty and before the menopause, which can cause irregular bleeding. The menstrual cycle may become longer or shorter and/or the periods may become lighter or heavier.

Another reason for irregular periods around puberty and the menopause is that the ovaries are not producing an egg every month.

Gynaecological problems

Irregular bleeding can also be due to unsuspected pregnancy (see below), early miscarriage or disorders (problems) of the womb or ovaries.

Thyroid disorders

A thyroid disorder is another possible cause of irregular periods (the thyroid gland produces hormones that maintain the body's metabolism). The doctor may test for a thyroid problem by checking the levels of thyroid hormones in the blood.


An intrauterine device (IUD) or contraceptive pill may cause spotting between periods. An IUD can cause heavy bleeding.

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


Bleeding when you have sex or heavy bleeding between periods could be a symptom of cancer of the cervix or womb, although this is rare. This can be diagnosed by examination and biopsy. Tests may include colposcopy, direct examination of the vagina and cervix and a pelvic scan.

^^ Back to top


Irregular periods are common during puberty or nearing menopause and treatment is usually not necessary.

If treatment is necessary, the type of treatment will depend on the reason for your irregular periods.

Changing your method of contraception

If you have recently been fitted with an intrauterine device (IUD) and you are experiencing irregular bleeding that does not settle within a few months, discuss changing to another method of contraception with your GP or practice nurse.

If you have started taking a new contraceptive pill that is causing irregular bleeding, you may be advised to change to another type of pill.

Treating polycystic ovarian syndrome

For overweight women with polycystic ovarian syndrome (PCOS), the symptoms can be improved by losing weight, which will also help with irregular periods. If you lose weight, your body does not need to produce as much insulin, which reduces testosterone levels and improves the chance of ovulation (releasing of the egg each month).

Other treatments for PCOS include anti-male hormone drugs and other hormone treatment.

Treating thyroid problems

Treatment for an overactive thyroid gland involves:

  • medicines that slow down the production of thyroid hormones,
  • radioactive iodine therapy, or
  • surgery to remove part of the thyroid gland 
  • The menstrual cycle should return to normal after these treatments. If it does not, go back to your GP.

Counselling and stress management

Stress or sudden weight loss may be diagnosed as a cause of irregular periods. Relaxation techniques, stress management or counselling (talking to a therapist) may be recommended

When should I seek help?

Talk to your doctor if you have any of the following changes in your periods:

  • You have very heavy periods, where you need to change your tampon or pad every hour or two, or you have to wear both a pad and a tampon.
  • Your periods last for longer than seven days.
  • There are fewer than three weeks between the start of one period and the next.
  • You have bleeding or spotting between periods. 
  • You are bleeding after sex.  

Trying for a baby

If you are having problems conceiving a baby due to an unpredictable menstrual cycle, treatment with synthetic hormones may help to achieve regular ovulation (monthly release of the egg). Discuss this with your GP.

^^ Back to top
“Pearn's Pharmacies, putting patients first”

Pearn's Pharmacy Services

Common Ailment Service

Primary Choice is a campaign to help the public choose the right health advice in the community.

Tell Me More


Repeat, one-off prescriptions. Collect in store or home delivery.

Sign Up

Funded Services

Browse our NHS funded services offered in our stores.

See Services


We are receiving an increase in the number of requests for delivery of medicines due to the COVID-19 pandemic.

Important Info

Find a GP   

Use our GP locator service and nearest Pearn's Pharmacy Branch

Search Now