What Causes Irregular Periods?

14 February 2020    by - Dr Demetri C Panayi

After puberty, a woman will have a regular menstrual cycle, with periods occurring around the same time every month. The average menstrual cycle is around 28 days, however, a cycle will vary between each individual person and can typically last for between 24-35 days.

Many women experience irregular periods (oligomenorrhea), such as starting earlier or later in their cycles, being particularly heavy or light, or lasting for a prolonged amount of time.

Your monthly cycle is often a good indication of your overall health, which is why it is important to keep track of your period and book a doctor’s appointment if it starts behaving erratically. Of course, there are various reasons as to why a period may become irregular, and not all will require medical attention.

Continue reading, as we discuss several common causes of irregular periods, what they might mean for your health and when you should see a doctor.

Hormonal contraception

One of the most common reasons for irregular periods is the hormonal changes caused by using contraception. The contraceptive pill, coil, implant and contraceptive patches can all cause irregular periods or may result in your period stopping altogether. If you switch contraceptive methods, this may also have an effect on your menstrual cycle.

That being said, many people continue with a normal, regular menstrual cycle when taking hormonal contraception. As there are a variety of types to choose from, it is important to discuss with your GP the contraceptive method which is right for you.


Around 1 in 5 UK women have Polycystic Ovary Syndrome (PCOS), which is a chronic, long-term condition whereby small cysts form on the ovaries, affecting their functionality. As women with PCOS do not ovulate or release an egg each month, the most common symptom is irregular or no periods. While infertility may also occur because of PCOS, many women find that they are able to conceive.


Endometriosis affects around 10% of women and is a condition in which the tissue which lines the uterus grows in areas outside of it. Endometriosis causes extremely painful, often irregular periods. Periods may be much longer than normal and people may encounter bleeding between them. There are many other symptoms of endometriosis, such as bowel problems, pain during sex, infertility and gastrointestinal pain.

If you are experiencing any of the above, you should speak to your doctor, as endometriosis is a chronic condition which can take many years to diagnose and seek treatment for.

Thyroid problems

If your thyroid is not functioning as it should, irregular periods can be a result of this. Thyroid disorders; hypothyroidism and hyperthyroidism, can also lead to extreme fatigue, weight gain and depression, amongst other symptoms.


Perimenopause occurs a few years before menopause begins, in which time a woman’s oestrogen levels will fluctuate, which can typically result in irregular periods. Spotting between periods, light or heavy periods, shorter or longer periods, or missed periods are all usual during the perimenopause years.

If, however, you start experiencing very heavy bleeding during this point in your life, you should speak to your doctor, as it could be a sign of another medical condition often mistaken for symptoms of the menopause.

Weight gain or weight loss

Extreme weight loss or weight gain in a short period of time can take its toll on the body. It can affect your hormones, throwing them off balance and leading to irregular periods. In certain people with very strict diets and low-calorie intakes, or who have started exercising excessively, periods may stop altogether.

If you have lost or gained a lot of weight recently and your period has become irregular or stopped, it is normally a good indication that you may not be of a healthy weight. Speak to your doctor for information and advice.


Stress doesn’t just affect your mood – in fact, it can have a direct impact on many areas, including your sleep cycle, your blood pressure, your libido and your menstrual cycle too. When we become particularly anxious or worried, the stress cortisol is released into the body, which may affect our oestrogen and progesterone levels, and, in turn, impact our menstrual cycle, causing a period to be late, early, or not show up at all.

Keeping stress levels to a minimum and finding effective mechanisms to help cope with day-to-day difficulties can help. Many people find that meditation and breathing exercises, a healthy diet, a good night’s sleep and low-intensity, calming work-outs, such as yoga or Pilates, can assist in reducing their stress levels.

When should you see a doctor for irregular periods?

Menstrual health is significant as it relates to several other areas, such as heart health, sleep, fertility, metabolism and more. As such, if your menstrual cycle is typically regular and your periods become irregular all of a sudden or you’re experiencing extreme period fatigue for seemingly no reason, then visiting a doctor is strongly advised, especially if you are under the age of 45.

If you notice bleeding after sex or between periods, or if you have extremely heavy periods (menorrhagia) or those that last for more than seven days, you should speak to your GP. Any of these symptoms can point to an underlying medical issue, such as an infection, a problem in the cervix, or in very rare cases, cancer.

If you have missed a period after having recent unprotected sex, then we recommend first taking a pregnancy test. If the test is negative and you continue to miss periods, you should also see a doctor. A missed period could be caused by hormonal changes and may require medical care.

Your doctor may refer you to a gynaecologist if your issue requires specialist knowledge, additional tests or treatment.

What treatment is available for irregular periods?

In the majority of women, irregular periods will normally settle down without the need for treatment. More often than not, a lifestyle change, such as eating a healthier, more balanced diet, or reducing stress levels, can be enough to help regulate the menstrual cycle.

However, women with more severe symptoms will need to seek medical treatment. The most common treatment method is being prescribed oral contraceptives, which can help to regulate the menstrual cycle and reduce problems like excessive or prolonged bleeding.

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