What causes irregular periods?
Short answer: Irregular periods result from disruptions to the hormonal cycle that controls ovulation and the uterine lining. Common causes include polycystic ovary syndrome (PCOS), thyroid disorders, stress or significant weight change, certain medications, breastfeeding, pregnancy, and perimenopause.
Explanation
Menstrual regularity depends on the hypothalamic–pituitary–ovarian axis and balanced estrogen and progesterone production. Anything that prevents regular ovulation (anovulation) — for example PCOS, functional hypothalamic amenorrhea from low body weight or heavy exercise, high prolactin, or thyroid disease — can make cycles irregular. Medications such as hormonal contraceptives, some antidepressants, and antipsychotics can alter bleeding patterns. Structural uterine problems (fibroids, polyps, adenomyosis) or intrauterine pathology can cause irregular or heavy bleeding. Pregnancy and postpartum lactation commonly stop or alter cycles, and perimenopause causes gradual cycle length changes. Persistent or severe changes (missing periods for several months, very heavy bleeding, bleeding between periods, or intense pain) should be evaluated by a clinician to rule out treatable causes.
Tips
- Track cycle length, bleeding days, and symptoms for several months to identify patterns.
- If sexually active and a period is missed, take a pregnancy test before assuming another cause.
- Discuss medications and supplements with your provider—some affect menstrual hormones.
- Address modifiable factors: manage stress, maintain a healthy weight, and avoid excessive exercise.
- See a healthcare professional for persistent irregularity, very heavy bleeding, severe pain, or if you have risk factors like obesity, acne, or excess hair growth (suggestive of PCOS).
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