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What Causes Irregular Periods?

What Causes Irregular Periods?

March 16, 2023

The average menstrual cycle usually lasts for 28 days, but it’s not uncommon for it to be a bit longer or shorter than that. 

After puberty, many menstruators tend to experience a regular menstrual cycle, meaning there’s a similar length of time between periods. However, it’s normal for your cycle to vary by a few days every time.

According to the American Academy of Family Physicians, 9-14% of menstruators have irregular periods from the time they get their first period to the start of menopause.

For various reasons, you may have irregular periods, so let’s dive into some of the most common explanations.

1. Increase in Stress

Did you know stress hormones can directly impact your menstrual cycle? Prolonged stress can cause you to have irregular periods or, in some cases, to skip your period entirely.

2. Medical Conditions

Some health conditions are connected to missed or irregular periods. They include:

  • Endometriosis
  • Pelvic inflammatory disease
  • Bleeding disorders
  • Uterine or ovarian cancer
  • Thyroid or pituitary gland disorders

3. Certain Medications

Specific medications can cause irregular periods. Some medications that may cause your period to be irregular include the following: 

  • Birth control pills, implants or injections
  • Steroids 
  • Blood thinners
  • Anti-epileptic drugs (AEDs)

4. Hormonal Imbalances

Several hormones play a huge role in your menstrual cycle. Because of this, an imbalance in one or multiple of those hormones can result in irregular periods. Certain hormone-related conditions that can cause irregular periods include amenorrhea and polycystic ovary syndrome (PCOS)

5. Significant Weight Loss or Gain

Gaining or losing a significant amount of weight can impact the production of your hormones (specifically estrogen), causing irregular periods.

When to See a Doctor

You don’t need to seek out medical advice if you’ve always had slightly irregular periods.

But you should see a doctor if… 

  • Your periods last longer than 7 days
  • You have periods more often than every 21 days
  • You have periods less often than every 35 days

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Sources: The American Academy of Family Physicians, Penn Medicine, Cleveland Clinic, Everyday Health & the NHS


Aunt Flow does not provide medical advice. This content is for informational purposes only. No material on this site is intended to serve as a substitute for professional medical advice, diagnosis or treatment. Please consult your doctor or a qualified health professional with any questions you may have. 

Stay in the flow — we’ll send you period positivity + timely updates on the menstrual movement.

claire coder,founder + ceo

claire coder,
founder + ceo

Hi! I’m Claire. I founded Aunt Flow after getting my period in public without the supplies needed.

At 18 years old, I dedicated my life to developing a solution to ensure businesses and schools could sustainably provide quality period products, for free, in bathrooms. Our products are made with organic cotton and we are constantly working to reduce our environmental impact! Since 2021, we've donated over 6 MILLION period products to menstruators in need. I call this people helping people. PERIOD.®