What Causes Irregular Periods?

Marie-Claire De Villiers
By Marie-Claire De Villiers
Romi Hector
Edited by Romi Hector

Published May 26, 2022.

Woman grimacing and holding calendar and sticky note that reads "SOS"

Most women have their period every 24 to 38 days, lasting anywhere between two and eight days. However, irregular periods are more common than most people think and can be caused by numerous factors.

Irregular periods (oligomenorrhea) are diagnosed when a menstrual cycle is shorter than 24 days, longer than 38 days, or changing length from month to month.

What Causes Irregular Periods?

Changes in Hormone Levels

Changes in estrogen and progesterone are the primary cause of irregular periods—the pattern of your period is changed by the fluctuating levels. These hormonal changes or disruptions may be caused by numerous factors, such as illness, menopause, perimenopause, puberty, stress, or environmental factors or changes.


Age plays a significant role in hormonal changes, particularly during puberty, menopause, and perimenopause.

  • Puberty Puberty usually occurs in girls between the ages of 10 and 14 and in boys between the ages of 12 and 16. At this time, hormone levels fluctuate—they haven't settled into regular patterns yet—causing irregular periods.
  • Menopause and perimenopause As hormones begin to slow down, they become irregular, interrupting women's regular cycles until their periods stop completely. Perimenopause is the phase of transition into menopause, and irregular periods are one of the first signs. Perimenopause and its irregular periods may last four to eight years. When a woman hasn't had a period for 12 months, she has entered menopause.

Certain Medications

Certain medications may affect women's hormones and thus on their periods. Every medication is different, and everyone responds differently to the same type of medication, so make sure to always ask your doctor about the potential side effects when you're trying something new and take others' experiences of a certain pill with a pinch of salt.

Some medications that can cause irregular periods include:

  • Antidepressants
  • Nonsteroidal anti-inflammatory drugs, or NSAIDs, such as ibuprofen, Motrin, or Advil
  • Blood-thinning medications, such as aspirin
  • Thyroid medications
  • Epilepsy drugs
  • Chemotherapy drugs

The pill, implants, patches, and IUDs suppress ovulation, but users may still experience vaginal bleeding and spotting once a month. In some women, bleeding may stop completely. Changes in the heaviness of bleeding and its regularity are common. Irregular bleeding caused by contraceptive medication is not harmful.

High Stress Levels

In some cases, high stress levels may cause an interruption in a woman's cycle. Hormones such as adrenaline and cortisol are released when a person is under stress, and these interfere with the hormones that regulate menstruation.

Medical Conditions

Certain medical conditions can cause hormone fluctuations and changes to regular period cycles. Some of these include:

  • PCOS (polycystic ovary syndrome)
  • Thyroid conditions such as hypothyroidism and hyperthyroidism
  • Uterine conditions such as uterine thyroids
  • Endometriosis
  • Cervical and endometrial cancer

Pregnancy and Breastfeeding

One of the first signs that may indicate pregnancy is a missed period. However, it should be noted that it is possible to have spotting or some bleeding and still be pregnant. However, please note that it is also advised that you see a doctor if you are pregnant and experience bleeding.

A breastfeeding woman might find that her period doesn't return for a few months or even a year after birth. Prolactin, the milk-making hormone, stops ovulation and, therefore, periods.

Poor Diet, Being Underweight, and Excessive Exercise

A bad diet causing a lack of essential nutrients and vitamins may cause an irregular cycle. Women who become clinically underweight may also notice their periods becoming irregular or stopping altogether. Excessive exercise can also have this effect.

Dancers and other athletes who utilize strict dieting and tend to over-exercise, along with women who have anorexia or bulimia, are more at risk of irregular periods, low bone mineral density, and osteoporosis.

How Do I Know if My Cycle Is Regular?

Take a look at our expert's comprehensive guide for more insight into the four phases of the menstrual cycle so you can start tracking yours now.