What Causes Irregular Period Cycles?

Jessica Lubahn 9 min read

What Causes Irregular Period Cycles?

Your cycle is off. 

It’s either early, late, or barely shows up. 

You’re tired of feeling out of sync. What gives?

Various things that can throw off your period — from physiological events to lifestyle factors, even medical conditions and hormonal disruptions. Whatever the reason, you want answers.

We’re diving into potential causes of irregular period cycles and how you can better prepare for “Aunt Flow” to make her appearance. 


what causes irregular period cycles

Table of Contents

An Overview of What Can Throw Off Your Period Cycle: 5 Common Factors to Consider

Most women have a period every 28 days, lasting from four to seven days. The average menstrual cycle ranges from 21 days to 35 days. 

Periods that … 

  • Occur less than 21 days or more than 35 days apart
  • Last longer than seven days
  • Are absent three or more cycles in a row; and
  • Present a much heavier or much lighter flow than usual

… are generally considered irregular

But what causes these abnormal cycles? Let’s explore five common factors that could be throwing off your period cycle. 

what can throw off your period cycle

#1: Physiological Events


The first sign of pregnancy for most women is their missed period. 

Once an egg has been fertilized and implanted into your uterus you stop ovulating. The hormones produced during pregnancy tell your ovaries to stop ovulating and your body holds onto your uterine lining to house your baby — resulting in a lack of a period. 

When the egg isn’t fertilized by a sperm, your uterus sheds its lining each month because no embryo needs to be housed during pregnancy — resulting in a period.

Alright, but why is it that when some women are breastfeeding, they don’t get a period for months at a time, sometimes even up to a year? 

Hormones may be to blame. Again. 

Prolactin, the hormone that tells your body to make milk, usually stops your body from ovulating. Physicians refer to this as lactational amenorrhea. It is not considered harmful because, for many women, menstruation begins shortly after breastfeeding slows down or stops completely. 

It’s important to note that although breastfeeding may cause your irregular or missing period, it’s not always the cause — and you may still conceive while breastfeeding. 

what causes an irregular period cycle


Perimenopause is the time “around menopause” when your body begins making the transition into menopause — which is the end of your reproductive years — and is also known as the menopausal transition. 

During the menopausal transition, your body produces less of the hormones that encourage ovulation, often resulting in irregular periods. 

You may experience:

  • Light or heavier bleeding
  • Longer or shorter periods
  • Months without periods
  • Changes in your PMS symptoms

#2: Lifestyle Factors

Poor Nutrition

Poor nutrition or not getting enough beneficial calories can throw off your period cycle.

When your body isn’t getting the right nutrients, it can put stress on your: 

  • Adrenal 
  • Hypothalamus; and
  • Pituitary glands

These are the glands that regulate the hormone balance throughout your body. 

Some of the most common nutritional deficiencies that cause your hormones to be disrupted include: 

  • Carbohydrates — that can disrupt your thyroid function while also lowering leptin levels throughout your body. Both of these hormones regulate your reproductive hormones and your period cycles. 
  • Folic acid studies show that folic acid plays a role in the length of menstrual cycles, and adequate amounts can help stabilize menstrual cycles. 
  • Healthy fats — healthy fats (specifically polyunsaturated fatty acids) support ovulation and hormone levels. 

Extreme Weight Gain/Loss

Gaining or losing extreme amounts of weight can affect your menstrual cycle. 

But how? 

Your weight — and the amount of fat on your body — can have a significant influence on the hormone levels in your body. Women who are underweight or do not have enough body fat may skip periods for months or have no period at all. 

Those who are overweight, with too much body fat, may have missed periods or periods that are heavy and last longer than their “regular” cycle. 

If body weight is throwing off your period cycle, achieving a healthy weight may be all it takes to regulate your body and your menstrual cycle. 

Excessive Exercise

Let’s start by saying that regular exercise typically isn’t the culprit for period disruption — excessive exercise, on the other hand, could be to blame. 

Female athletes, dancers, and those who train intensively may experience irregular cycles — and in some cases resulting in Amenorrhea

What happens is this: 

When women exercise too much, their bodies experience what we’ll refer to as a “mismatch” between the amount of energy they consume and the amount of energy they expend. 

When you don’t have enough energy available, your body looks for ways to conserve energy. But what does conserving energy have to do with your hormones? A lot. 

One of the ways your body will conserve energy is by slowing down your metabolism, in turn causing ovulation to stop. This allows your body to store that energy and use it to fuel other parts of your body. 

irregular period cycle causes

#3: Medications That Interrupt Hormones

Birth Control

Although birth control is often used to help women regulate their periods, it can also throw your period cycle off — especially in the first few months of taking it.

Breakthrough bleeding is especially common when starting a new type of birth control. For some women, hormonal birth control may even cause their periods to disappear. 

Non-hormonal options, like the copper IUD, have been known to cause longer, heavier periods. 


Selective serotonin reuptake inhibitors (SSRIs) may play a role in your irregular periods.

SSRIs can cause high levels of prolactin (the same hormone that tells your body to make milk after having a baby) to be released throughout the body. High prolactin levels inhibit the release of hormones required to release eggs. 

No eggs = no period. 

Other antidepressants act on different biological targets in your brain called norepinephrine-dopamine reuptake inhibitors and nicotinic receptor antagonists. 

Those taking these antidepressants may experience:

  • Spotting
  • Shortened cycles; or
  • Amenorrhea

Blood Thinners

Blood thinners (anticoagulants) do not necessarily cause your menstrual cycle to be irregular, but they sure can mess with your flow. 

Nearly 70% of women on anticoagulants are affected by heavy menstrual cycles. 

#4: Medical Conditions

Thyroid Disease

Your thyroid gland — the little butterfly-shaped gland at the front of your neck — can greatly influence your period cycle. 

Hypothyroidism (when your body produces too little thyroid hormone) can cause: 

  • Heavy periods
  • Frequent periods
  • Absent periods

Hyperthyroidism (when your body produces too much thyroid hormone), on the other hand, can cause: 

  • Infrequent periods
  • Absent periods
  • Light/short periods

If you are struggling with thyroid disease, your physician may prescribe medication that not only helps your thyroid function properly but may also regulate your menstrual cycle. 

Polycystic Ovary Syndrome (PCOS)

One of the most common signs of Polycystic Ovary Syndrome (PCOS) is irregular (or few) periods. 

PCOS is a hormonal imbalance that is caused by your ovaries — the ovaries produce excess male hormones known as androgens.

As a result of this imbalance, women often have irregular menstrual cycles, missed periods, and sporadic — or nonexistent — ovulation. 

Ovarian Failure

Ovarian failure is a condition when a woman’s ovaries stop functioning normally before the age of 40. There are two types of ovarian failure:

  1. Primary ovarian failure: the ovaries are not functioning normally. 
  2. Secondary ovarian failure: the ovaries function normally, but hormone signals struggle to get from the ovaries to the brain. Secondary ovarian failure is typically caused by diseases of the hormone glands. 

Women with ovarian failure may experience normal periods, while many experience irregular or absent cycles. 

#5: Structural Abnormalities

Several different structural abnormalities may cause irregular periods, the most common being:

  • Uterine fibroids — these fibroids that develop in the uterine cavity may affect the uterus lining, causing heavy and irregular periods
  • Pelvic Inflammatory Disease  — as a bacterial infection affecting the female reproductive system, bacteria can spread through the uterus. Those with PID may experience painful, irregular periods and other symptoms like foul-smelling discharge, fever, nausea, and pain in the lower abdomen.

Consult your physician if you are concerned that a structural abnormality may be to blame for your irregular cycle. They can help you create a plan to determine if any abnormalities or health conditions are to blame for your thrown-off cycle. 

How To Prepare for Irregular Cycles

Unsure of if you’re dealing with an irregular period? Consider using a period tracking app. 

These apps generally require users to track their menstrual cycle for a few months — they may ask for the first day of your last period, and the last day of your last period for 2-3 months. 

Once you’ve input the required information, the app will calculate when your upcoming periods should be. If you notice that your periods aren’t occurring regularly, contact your physician.  

Knowing what causes irregular cycles may give you peace of mind — but it won’t necessarily help you prepare for your period to arrive. 

Thankfully, there’s a solution for that, too. And no, it doesn’t involve constantly wearing panty-liners.

Be Prepared Whenever Your Period Makes Its Appearance With ONDR’s Leak-Proof Underwear

Introducing ONDRwear, ultra-absorbent, ultra-sleek, period-proof underwear. 

ONDR period underwear are designed to:

  • Absorb everything without feeling bulky
  • Keep you feeling dry by wicking away wetness
  • Control odors using a patent-pending plant-based liner
  • Be leakproof to keep your clothes free of stains
  • Protect the environment by reducing waste

Don’t let the fear of the unknown stop you from doing what you love. Shop ONDR today and get back to feeling comfortable, even when your period makes a surprise visit. 

what can throw off your period cycle


The content in this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.