10 Common Causes of Irregular Periods

Author: Ifeoma Ikechukwu, Pharm.D

Medical Reviewer: Sheeza Khan, M.Phil. Zoology (Life Sciences) 

Highlights 

• Your period can be irregular if your cycle is below 21 or above 35 days, or if bleeding is unusually heavy, light, or painful.
• Common causes include stress, excessive exercise, the early years after menarche, pelvic inflammatory disease, breastfeeding, PMOS, and major weight changes.
• Abnormal menstrual bleeding occurs in about 14% to 24% of women of pubertal age and above.
• You may experience temporary changes in your menstrual cycles, but if they persist, seek medical attention.
• Irregular menstruation can be effectively managed by addressing the underlying cause either through lifestyle modification or the use of medications.
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• Introduction

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• Irregular periods are characterised by very heavy or unusually light flow, cycles that are longer or shorter than normal, or periods accompanied by symptoms like severe abdominal cramps, nausea, or vomiting [1]. Your period can also be irregular if it lasts more than 8 days or if you miss 3 months.  
• An average cycle, the period between the first day of your menstrual period and the first day of the next, is about 28 days. Cycles that last between 21 and 35 days are generally considered normal [2]. However, what is considered normal can depend on your age. For instance, for the first few years after your first period, your cycle range might be above 35 days. Between the ages of 20 and 30, the normal range can last from 21 to 35 days. As one approaches menopause (between the 40s and 50s), cycles may become very short (less than 21days). 
• A cycle becomes abnormal or irregular if it falls outside these ranges. Studies show that about 14% to 25% of women of puberty age and above have irregular menstrual cycles [3]. 
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• You might experience temporary changes in your menstrual cycle if the hormonal system that regulates it is disrupted. As a result, ovulation is delayed and the bleeding pattern changes. Common factors that contribute to this include stress, intense exercise, and medical conditions like Polyendocrine Metabolic Ovarian Syndrome (PMOS). 
•  If these changes become persistent or occur frequently, it could be from underlying causes that may require medical attention.
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• 10 Common Causes of Irregular Periods

1. Breastfeeding 

• During Breastfeeding, prolactin levels (a hormone that supports milk production) are increased. This suppresses ovulation by slowing the production of the hormones that cause ovulation (Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH)). This process can cause irregular or missed periods. It is important you know that ovulation can happen before your first postpartum period, which means you can get pregnant even before your period.
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• 2. Puberty

• The hormonal communication network comprising the Hypothalamic -Pituitary-Ovarian (HPO) axis controls Ovulation.  After the occurrence of menarche, the first menstrual period, you may often experience irregular periods because this axis is not fully mature. A study on Menstrual Disorders in Adolescence noted that even 2 years after menarche, up to 85% of cycles remain anovulatory [4], meaning that the axis is not mature enough to support ovulation. 
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• 3. Perimenopause 

• This refers to the period before menopause, approximately between 40 and 50 years of age. Periods become irregular because the ovaries stop releasing eggs regularly during this time.
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• 4. Stress and Anxiety 

• When you are stressed, your body releases a hormone known as cortisol. High, sustained cortisol levels interfere with the normal functioning of the hypothalamic-pituitary-gonadal axis (HPG), the axis that regulates the menstrual cycle. This disrupts the hormonal balance required for regular ovulation and menstruation. 
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• 5. Weight loss or Weight Gain

• Significant weight loss or gain can suppress ovulation. A study recorded that obese adolescent females experience hyperandrogenism (excess levels of male sex hormones), leading to irregular or absent menses [5]. On the other hand, rapid weight loss or low energy can alter your cycle because your body goes into survival mode, stopping any non-essential activities, including the production of reproductive hormones.
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• 6. Thyroid Disorders

• Thyroid disorders, whether hypothyroidism (low levels of thyroid hormone) or hyperthyroidism (high levels of thyroid hormone), interact with menstrual regulatory hormones, leading to missed or irregular periods.
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• 7. Polyendocrine Metabolic Ovarian Syndrome (PMOS)

• This was previously called PCOS. This medical condition can cause your ovary to produce large amounts of androgens, leading to a delay in ovulation, which can cause irregular bleeding. PMOS affects nearly 10-13% of women of reproductive age, and about 70% of women with this condition are unaware of it. 
• Other hormonal problems, such as elevated prolactin levels, can also affect your menstrual cycle.
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• 8. Excessive Exercise

• Intense exercise without sufficient calorie intake can lead to irregular periods. Not consuming enough calories after exercise can make your brain sense physical stress, which can shut down reproductive hormone production. 
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• 9. Hormonal Contraception 

• Some contraceptives, whether pills, injections, or implants, can alter your bleeding patterns. This is because they can change the levels of the hormones in your body and can prevent ovulation and affect the shedding of the uterine lining.

• 10. Pelvic Inflammatory (PID)

• PID is the inflammation of the upper reproductive organs, including the uterus, fallopian tubes, and ovaries. It is often caused by bacteria from sexually transmitted diseases. If left untreated, it can alter your menstrual cycle, leading to spotting, delayed periods or severe cramps. 
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   When Is an Irregular Period Normal?
  

• Though irregular periods can be a concern, they're sometimes normal. This happens during the: 
  • First few years after the onset of menses,  
  • Around perimenopause
  • During breastfeeding. 
  • When using some hormonal contraceptives
• Most of the time, this might not be due to any major problem. However, when the changes become prolonged, like bleeding constantly for more than 8 days or no period for 90 days, you should visit a specialist for a checkup.

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  When Should You See a Doctor?

• You should consider seeing a doctor if your period deviates from its usual pattern. For instance:
  • Missing your period for about 3 months.
  • Unusually heavy bleeding or menorrhagia (soaking one or more pads or tampons every hour for two hours in a row or heavy bleeding lasting more than 7 days)
  • Severe pain that doesn't subside with medications
  • Bleeding for more than 8 days
  • A cycle that is shorter than 21 days or longer than 35 days, or depending on your age as described above.
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• Also, if you notice that you often become dizzy, have a feeling of fainting, or have severe abdominal pain, consult your doctor immediately, as this can suggest an underlying cause that may be due to significant blood loss. 

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  How Are Irregular Periods Diagnosed?

• A healthcare professional can ask some questions, perform physical examinations, and carry out some tests to diagnose irregular menstrual periods.
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• History 

• Your clinician can start by asking you these questions:
  • When did you first observe the change?
  • How heavy is your bleeding?
  • Are you pregnant?
  • How painful is your period? 
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• Questions about stress, eating and weight changes, exercise, contraceptive use, PCOS, and history of thyroid disease can be asked to diagnose the cause of the irregularities properly.
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• Physical Examination 

• Your doctor will check your vital signs, body mass index (BMI), and can look out for signs of anaemia and thyroid disease. He can also conduct a pelvic examination where he inspects your reproductive organs like the cervix, vulva, vagina, and the uterus.
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• Tests

• Depending on the suspected cause, your physician may order some tests. Common tests include:
  • Pregnancy test
  • Blood test (to check for hormones like thyroid-stimulating hormone (TSH), prolactin, FSH, LH, and androgen (male hormone) levels)
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• Other more diagnostic tests can be used to check for changes in the shape and size of your reproductive organs, detect abnormal cells and identify hormonal issues. These include:
  • Pelvic ultrasound: This test uses sound waves to create a picture of your pelvic organs to check for fibroids, cysts, and PID.
  • Endometrial biopsy: This can be used to check for endometriosis, hormonal imbalance and precancerous cells.
  • Hysteroscopy: This checks for any non-cancerous growth like fibroids.
  • Transvaginal ultrasound: This can be used to examine your womb to check the thickness of your uterine lining and to look for the presence of polyps (growths in the lining of the uterus)
  • Sonohysterography: This is similar to transvaginal ultrasound and provides a more clearer view of the womb.
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• These tests check for any underlying ovarian or uterine causes. 
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• How Can Irregular Periods Be Managed?

• Irregular menstruation can be managed by first understanding the underlying cause. In many cases, physicians look for the cause of the abnormal bleeding and address it, rather than the bleeding itself.
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• They can manage the condition by recommending lifestyle changes, medications, or surgery to treat the underlying cause.
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• Lifestyle Management 

• Lifestyle changes may help when menstrual irregularity is related to factors such as inadequate energy intake, significant weight changes, or excessive exercise. Nutritional changes and moderate exercise can be recommended to restore regular periods. A study reported that women who combine balanced nutrition with consistent moderate activity experience improved menstrual regularity [6]. 
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• Medications

• Doctors prescribe medication when lifestyle changes do not work.  Hormonal therapies like combination pills and progestins are commonly used to manage irregular periods.
• Combination pills contain estrogen and progesterone that work to prevent your ovaries from releasing eggs. Progestins are compounds that act like the progesterone hormone and ensure the uterine lining is not too thick, thereby preventing heavy or abnormal menstruation. These drugs work to regulate cycles and control abnormal bleeding. They come as either oral pills, a vaginal ring, or an intrauterine device. 
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• Conditions like PMOS- related irregularities can be managed using hormonal therapies and insulin-sensitising drugs like Metformin, with the primary aim of balancing hormonal levels and restoring regular periods. Metformin, though primarily used for type 2 diabetes, can be prescribed by your doctor to combat insulin resistance, which is a common feature in PMOS. By lowering insulin levels, it reduces its effect on androgen production, which helps to restore regular cycles. 
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• Your physician can also prescribe other medications like NSAIDS (non-steroidal anti-inflammatory drugs) for pain or painful bleeding, or tranexamic acid to treat heavy menstrual bleeding. Antibiotics can also be prescribed if your condition is due to an infection like in Pelvic inflammatory disease.
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• Surgery

• Some surgical options can be recommended for menstrual irregularities. This can be subject to the cause, your age, and your desire to get pregnant.  These include:
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  • Endometrial ablation: This is done to destroy the lining of your uterus to reduce how much you bleed during your periods. Your health professional can recommend this when you have heavy menstrual bleeding. However, if you would like to get pregnant in the future, this option will be inappropriate for you.
  • Myomectomy: This surgery option is used to remove fibroids from your womb.  It keeps your uterus, as well as your chances of conceiving in the future.
  • Hysterectomy: During this procedure, your uterus is removed, particularly if your uterus has been severely damaged. You will not be able to get pregnant after this surgery and will stop having menstrual periods.

• Conclusion

• Irregular periods can arise from cycles that fall below or above the normal range and can be caused by a variety of factors. Though occasional changes can be normal, persistent occurrences may suggest underlying conditions. 
• Tracking your usual pattern and noticing when changes become unusual can help you know when to seek timely medical care. Early medical evaluation can help identify the cause, inform management approaches, and prevent further complications.
• Most cases of irregular periods improve with lifestyle changes or medical care. If your periods remain irregular, see a healthcare professional.

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• References

• 1. Mittiku YM, Mekonen H, Wogie G, Tizazu MA, Wake GE. Menstrual irregularity and its associated factors among college students in Ethiopia, 2021. Front Glob Womens Health. 2022;3:917643. doi:10.3389/fgwh.2022.917643. Available from: https://www.frontiersin.org/journals/global-womens-health/articles/10.3389/fgwh.2022.917643/full
• 2. National Health Service (NHS). Irregular periods [Internet]. London: NHS; 2026 Jun 26 [cited 2026 Sep 20]. Available from: https://www.nhs.uk/symptoms/irregular-periods/
• 3. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). What are menstrual irregularities? [Internet]. Bethesda (MD): National Institutes of Health; 2017 Jan 30 [cited 2026 Sep 01]. Available from: https://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/irregularities
• 4. Anthon C, Steinmann M, Vidal A, Dhakal C. Menstrual disorders in adolescence: diagnostic and therapeutic challenges. J Clin Med. 2024 Dec 16;13(24):7668. doi:10.3390/jcm13247668. Available from: https://pubmed.ncbi.nlm.nih.gov/39768589/
• 5. Itriyeva K. The effects of obesity on the menstrual cycle. Curr Probl Pediatr Adolesc Health Care. 2022;52:101241. doi:10.1016/j.cppeds.2022.101241. Available from: https://pubmed.ncbi.nlm.nih.gov/35871162/
• 6. Hosabettu S. Irregular menstrual periods as a result of poor diet and physical activity: a review. Int J Multidiscip Res. 2025 Nov-Dec;7(6):1-4. [cited 2026 Sep 17]. Available from: https://www.ijfmr.com/papers/2025/6/63581.pdf 

Disclaimer:
The information provided on this website is for general educational and informational purposes only. It is not intended to replace 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.

Published September 30, 2026