What Causes Irregular Periods?

Dr Kathryn Basford

Medically reviewed by

Dr Kathryn Basford

Last reviewed: 13 Jan 2022

2 women walking by the beach talking about irregular periods

Irregular periods can be caused by:

  • the natural hormones in your body as you age
  • medicines you take, such as the contraceptive pill
  • medical conditions you might have, such as fibroids
  • whether or not you are pregnant
  • changes to your body weight or body fat
  • changes to what you’re eating on a daily basis
  • exercise
  • stress

Whatever the cause, your period is unique to you and it might be time to take action if your irregular periods are affecting how you feel about yourself.

What are irregular periods?

Irregular periods can mean different things to different people. For you it might mean that it:

  • has come earlier than you expected
  • is later than normal
  • is much shorter than usual
  • lasts a lot longer than you’re used to
  • does not happen at all

Another sign your period might be irregular is how much you bleed compared to your normal period bleed. If you’re not bleeding as much or bleeding a lot more than you normally do, this counts as an irregular period.

If your period is more or less painful than usual and you notice your periods are becoming irregular, it may be a sign that something has changed and needs to be checked by a healthcare professional.

Should I be worried if my periods are irregular?

There is no need to worry if you have an irregular period every now and again. But if your periods are unusually irregular or something does not feel right, you may want to have a health check to see if you:

  • are pregnant
  • have developed a health condition, such as polycystic ovaries, polyps or fibroids
  • are having side effects from a medication you are taking
  • need to change your contraceptive pill

Once you have seen a healthcare professional, such as a doctor, you can then take action to regulate your period. Getting the right advice will make sure you’re off to the right start, so you will not have to worry.

Reasons for irregular periods

There are many reasons for irregular periods, and they depend on what stage you’re at in life. Your period will change as you get older and it will eventually stop happening. But it’s good to know what the reason for an irregular period is in the first place, so you can be confident that you’re healthy and well.


If you’ve just started getting your periods, you might find that your body is trying to get into a regular rhythm. So it’s normal to have irregular periods. As you get older, your period will tend to happen consistently every 3 to 5 weeks. Then, when you start to reach menopause, your periods will become irregular again. You’ll have fewer periods and may go months without one.

Hormonal contraception

Taking the pill can make your periods irregular because of the hormones they contain. Progesterone based hormonal contraceptives, such as the mini pill, hormonal IUD or implant, can stop your period altogether. With the combined pill or contraceptive patch, you might get lighter periods. With any type of hormonal contraception you can get ‘breakthrough bleeds’, and you should see a doctor if these last longer than a few days.

The intrauterine device (IUD – a coil without hormones)

The intrauterine device (IUD) is also known as a copper IUD or ‘the coil’. It’s hormone-free, but it can make your periods irregular. Although it protects you from pregnancy straight after it’s put in, you might get random bleeds and cramps. A common side effect of the copper IUD is heavy periods and pain during your first few months. If these do not improve, you may need to consider removing it and trying an alternative.


Fibroids are lumps of cells that grow in or around the walls of your womb (uterus). Sometimes they can grow into your womb too. They’re usually not cancerous and cannot spread to other parts of your body, so we call them ‘benign growths’. Fibroids can cause heavy periods (where you bleed a lot), painful sex and irregular periods. You might feel pain or heaviness in your lower tummy area if you have fibroids. See a doctor if you have these symptoms, as fibroids might affect your ability to have a baby in future.


Polyps are glands that have grown a bit too big and start to stick out into the space of your womb. You can get polyps that grow and hang out of the entrance to your womb, where your cervix is. You might not know that you have polyps but a doctor might find them by doing a speculum exam to look at the entrance to the womb or on a scan. Polyps can cause heavy bleeding and irregular periods. When you have polyps, you might find it difficult to get pregnant.


Normally, the lining of your womb (the endometrium) sits on top of a layer of muscle that makes up the walls of your womb. In adenomyosis, the lining of your womb is inside this layer of muscle instead. This can cause irregular periods that are painful, or heavy. You might also get pelvic pain with adenomyosis. To see if you have adenomyosis, you have to go to a doctor that can have a look at the inside of your womb. Adenomyosis is not a type of cancer, and the cause might be something to do with:

  • genes that run in your family
  • your immune system
  • hormones that you naturally produce

Changes in ovulation

Ovulation is when you release an egg from your ovaries, and any change in this activity can lead to irregular periods. You normally release an egg every month during your menstrual cycle, but sometimes you might miss a month. It’s impossible to know when this happens, but it might be a reason why your period seems a bit off between one month and the next.

Issues with blood clotting

Blood clotting is when the cells in your blood stick together and form a lump. There are certain medicines, like aspirin, warfarin or rivaroxaban, that can make your blood thinner and stop blood clots from happening. If you take these blood thinners, your period bleeds might be more irregular and they could be heavier too. When your blood does not clot as it should, your periods can last longer than usual. Apart from medication, you might have a medical condition that affects how your blood clots. You can find out if you have a problem with your blood clotting by getting a blood test.


When you are pregnant, your periods will start to get lighter and stop completely. However, it’s still possible for you to have a bleed every now and again. If you find you start bleeding and get cramps while you are pregnant, speak to your midwife or a doctor for advice. Your pregnancy will be unique to you, and to have a safe pregnancy you should go to your regular check up appointments. Mention in as much detail as you can everything that you’ve been going through, and they will do their best to help you.

Other medical conditions

Polycystic ovary syndrome (PCOS) is another medical condition that can cause irregular periods. PCOS is when your body produces too many male hormones, known as androgens. There might also be little growths on your ovaries filled with fluid. You should speak to a doctor if you think PCOS might be causing your irregular periods, especially if you:

  • gain weight
  • are losing some of your hair or notice it’s not as thick as usual
  • start to grow hair on your face, chest or back
  • have oily skin or start to develop acne
  • find it difficult to get pregnant

Apart from PCOS, you might have another medical condition that could be causing irregular periods.

Why does contraception sometimes cause irregular periods?

There are different types of contraception that can sometimes cause irregular periods.

Hormonal contraception contains one or two types of female sex hormones that are either the same as or similar to what you naturally produce, oestrogen and progesterone.

The combined pill, contraceptive patch and vaginal ring all contain oestrogen and a form of progesterone. You normally use them for 3 weeks in a row and then have a 1 week break. You’ll have a withdrawal bleed during this 1 week break which is like a period, but will probably be lighter, shorter and less painful than your natural period. As a side effect, you can get bleeding at random times during your first few months of using this type of contraception. These irregular bleeds should improve over time. You also have the option of skipping your 1 week break and taking 3 cycles back to back if you want to delay your period.

The mini pill, contraceptive implant, depot injection and hormonal IUD are all types of contraception that only contain progestogen. It can take some time for your body to get used to them, and they can stop your periods completely for months or years. You might have breakthrough bleeds at random times when the lining of your womb starts to break down. This might happen every so often, but if it lasts longer than a week or you feel like you’re bleeding a lot, see a doctor as soon as you can.

The copper IUD can cause heavy, painful and irregular periods because it is inside your womb and has contact with the lining of your womb. This is to prevent an egg from implanting, which stops you from getting pregnant.

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Can you get pregnant with an irregular period?

You can get pregnant with an irregular period. Even if you have irregular periods, there’s a high chance that you’re still releasing an egg from your ovaries every month. This means you do need to use contraception, such as the pill, if you want to avoid getting pregnant while having unprotected sex. It’s also a good idea to use condoms to prevent sexually transmitted infections (STIs), as irregular periods do not protect you from STIs either.

If you have irregular periods and you are trying to get pregnant, it can make it harder to get pregnant because you might not be ovulating (releasing an egg) or it might be harder to know when you are ovulating. Having sex regularly, every couple of days, can help. If you are worried, speak to a doctor about getting pregnant.

Regulate your period with the combined contraceptive pill

If your periods have changed or become irregular you should see a doctor so they can find out what the cause for this is. Depending on the reason for the irregular periods, they might suggest different ways to regulate your periods.

Your doctor might recommend the combined contraceptive pill to regulate your bleeding pattern. The combined pill contains 2 hormones, a type of oestrogen and progestogen. These mimic the naturally occurring hormones that control your menstrual cycle. By taking a steady dose of hormones, you will be stopping your natural period from happening and preventing pregnancy.

When you take the combined pill to regulate bleeding, you will have a 7 day pill free break at the end of each 21 day strip of pills. During these 7 days, you should have some withdrawal bleeding.

Each pack of the combined pill contains 3 strips, which is a 3 month supply. After 3 months you can stop taking the pill to see if the spotting has stopped and your periods naturally become regular. You can also choose to continue taking the combined pill, especially if you want to use it for contraception.

The mini pill (progestogen only pill) cannot be used to regulate your period. This is because it must be taken every day which means you will not have a 7 day break.

If you’re using contraception that could make your periods irregular, you might be able to try changing to a different type of contraception to see if this suits you better.

You may also need to have a look at lifestyle changes. If you have PCOS, weight loss can help to regulate your periods, so eating healthily and exercise can help.

Medically reviewed by:
Dr Kathryn Basford Accreditations: MB, ChB, MPH

Dr Kathryn Basford is a qualified GP who works as a GP in London, as well as with ZAVA. She graduated from the University of Manchester and completed her GP training through Whipps Cross Hospital in London.

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Last reviewed: 13 Jan 2022

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