What causes irregular periods and what you can do about them

By Sina Hartung, MMSC-BMI, Harvard Medical SchoolReviewed by Eureka Health Medical Group
Published: July 9, 2025Updated: July 9, 2025

Summary

Irregular periods happen when the delicate feedback loop between the brain, ovaries and uterus is disrupted by stress, weight changes, hormones, medications or underlying conditions such as polycystic ovary syndrome or thyroid disease. Pinpointing the exact trigger requires tracking cycles, checking key labs and reviewing medications. Most causes are treatable once identified, so unexplained changes lasting three cycles or more deserve medical attention.

Why do menstrual cycles become irregular?

A normal menstrual cycle runs 24-38 days, but one in three women will experience irregularity at some point. "The menstrual clock is set by hormones that start in the brain, so anything that shifts that clock—stress, diet, illness—can change the timing," explains Sina Hartung, MMSC-BMI.

  • Hormone signals start in the brainThe hypothalamus releases GnRH, which tells the pituitary to secrete FSH and LH; any disruption here can shorten or lengthen a cycle.
  • Stress hormones override reproductive hormonesHigh cortisol from chronic stress can suppress ovulation, leading to skipped or late periods in up to 20 % of college students during exams.
  • Weight loss or gain changes estrogen levelsLosing more than 10 % of body weight in 6 months lowers leptin and estrogen, commonly halting periods (functional hypothalamic amenorrhea).
  • Common endocrine disorders play a rolePCOS affects about 10 % of reproductive-age women and is the leading medical cause of cycles longer than 45 days.
  • Some medications interfere with ovulationAntipsychotics, high-dose steroids and the copper IUD are all documented to cause cycle length changes in clinical studies.
  • Puberty and perimenopause naturally disrupt cycle timingIrregular bleeding is common in the first few years after menarche (around ages 9-14) and again during perimenopause (around age 50) because hormone levels rise and fall unpredictably. (CClinic)
  • Thyroid imbalance can delay or shorten periodsBoth under-active and over-active thyroid conditions are listed by the NHS as medical causes that disturb ovulation and lead to unpredictable cycles. (NHS)

References

When should irregular bleeding make you worry?

Most cycle hiccups are harmless, but certain patterns point to serious issues. The team at Eureka Health cautions that "heavy bleeding soaking through a pad every hour or bleeding after sex needs prompt evaluation."

  • Bleeding more than 80 mL per cycle signals menorrhagiaIf you double-up pads, pass clots larger than a quarter or become anemic, see a clinician within a week.
  • Bleeding between periods may indicate structural problemsPolyps, fibroids, or—rarely—cervical cancer can cause mid-cycle spotting; a pelvic ultrasound is warranted.
  • Sudden cycle changes after age 40 require evaluationPerimenopause is common, but endometrial hyperplasia or cancer must be ruled out if cycles are <21 or >45 days.
  • Severe cramps with irregular cycles can equal endometriosisEndometriosis affects 1 in 10 women and often presents with both pain and timing changes.
  • Positive pregnancy test with bleeding is an emergencyEctopic pregnancy causes irregular bleeding plus pelvic pain and needs same-day care.
  • Hourly pad or tampon saturation is an urgent warning signCleveland Clinic states that soaking through one or more pads or tampons in an hour for several hours in a row merits immediate medical attention. (ClevelandClinic)
  • Bleeding after intercourse signals possible cervical or uterine issuesThe same Cleveland Clinic guidance lists spotting after sexual intercourse as a red-flag symptom that should be promptly evaluated by a healthcare professional. (ClevelandClinic)

References

How do underlying conditions like PCOS or thyroid disease disrupt your cycle?

Specific medical disorders alter hormone levels that regulate the uterine lining. "Identifying the root condition is the fastest route to a predictable cycle," notes Sina Hartung, MMSC-BMI.

  • Polycystic ovary syndrome raises androgensHigh LH and insulin resistance prevent a mature egg from releasing, so the uterine lining builds up longer than 35 days.
  • Hypothyroidism lengthens cyclesLow thyroid hormone elevates prolactin, which can delay ovulation; 23 % of women with untreated hypothyroidism have cycles >40 days.
  • Hyperthyroidism shortens cyclesExcess thyroxine speeds up follicle development, sometimes causing periods every 21 days or less.
  • High prolactin from a pituitary adenoma stops periodsProlactin levels over 100 ng/mL inhibit GnRH, leading to amenorrhea in 90 % of affected women.
  • Perimenopause causes erratic estrogen spikesFrom age 40 onward, follicle count drops and estrogen surges unpredictably, leading to skipped periods then heavy bleeds.
  • PCOS affects up to 12 % of reproductive-age womenWith prevalence hovering around one in eight women, PCOS is the most common endocrine disorder behind cycle irregularity and can reduce the number of periods to fewer than nine per year. (FWCJax)
  • Thyroid and prolactin disorders sit high on NIH’s checklist for cycle evaluationThe NICHD notes that clinicians routinely rule out thyroid dysfunction and elevated prolactin when investigating irregular periods because these hormonal conditions commonly disturb ovulation and bleed patterns. (NIH)

References

What can I do at home to stabilize my cycle?

Lifestyle tweaks often smooth out mild irregularities within three months. The team at Eureka Health emphasizes, "Cycle tracking is the single best self-care tool—it transforms vague symptoms into actionable data."

  • Track cycle dates and flow detailsUse a calendar or app to log first day of bleeding, flow intensity and symptoms; patterns guide testing and treatment.
  • Aim for 7–9 hours of sleep nightlyWomen sleeping under 5 hours have 31 % higher odds of long cycles compared with those sleeping 7 hours.
  • Maintain a stable, healthy weightBody fat under 17 % or rapid gains over 30 BMI both disrupt ovulation; a gradual ±5 % weight change is safest.
  • Manage stress with evidence-based toolsA 10-minute daily mindfulness session lowered cycle length variability by 2.3 days in a small RCT.
  • Review medications with a pharmacistAsk whether any current drug lists irregular bleeding as a side effect and discuss alternatives if needed.
  • Sip ginger tea three times dailyBoiling crushed ginger for 5 minutes and drinking the infusion after meals up to three times a day is cited as a simple way to encourage more regular bleeding while easing cramps. (Practo)
  • Avoid very low-carb eating patternsGreatist notes that drastic carbohydrate restriction can disrupt hormones; the Dietary Guidelines advise keeping 45–65 % of total calories from carbs to support a predictable cycle. (Greatist)

References

Which lab tests and treatments will my clinician consider?

Objective data confirms the cause of irregular periods. "Ordering targeted labs prevents unnecessary ultrasounds and speeds up care," says Sina Hartung, MMSC-BMI.

  • Serum hCG is always firstPregnancy must be ruled out; even a light period can occur with an ectopic pregnancy.
  • Day-3 FSH, LH and estradiol gauge ovarian reserveAn FSH over 20 IU/L suggests diminished reserve and impending menopause.
  • TSH and free T4 screen for thyroid diseaseTreating hypothyroidism normalizes cycles in 70 % of women within 6 months.
  • Prolactin level checks for pituitary adenomaLevels above 25 ng/mL prompt an MRI to locate a microadenoma.
  • Hormonal contraception or metformin may be offeredCombined pills regulate bleeding in PCOS, while metformin improves ovulation in insulin-resistant women—always under physician supervision.
  • PALM-COEIN classification steers imaging versus lab workUsing PALM-COEIN, clinicians distinguish structural causes like polyps or fibroids (“PALM”) from hormonal or iatrogenic issues (“COEIN”), reserving ultrasound or hysteroscopy for the structural group and avoiding unneeded scans when labs alone will suffice. (Science.gov)
  • Stop hormonal birth control 3 months before a PCOS hormone panelAccurate LH, FSH and androgen values require being off pills or other hormonal contraception for about 3 months; otherwise results can be falsely low or high, warns the PCOS testing guide. (Bloomful)

References

Can Eureka’s AI doctor clarify why my periods are off?

Eureka’s AI doctor analyzes your symptom history and risk factors in seconds. The team at Eureka Health explains, "Our algorithm flags whether thyroid, prolactin or PCOS labs make sense before your next visit."

  • Instant pattern recognition from cycle logsUpload three months of data and the AI calculates average cycle length, variability and predicted ovulation windows.
  • Personalized lab recommendationsIf your history matches PCOS criteria (irregular cycles plus acne or excess hair), the AI suggests an androgen panel and fasting insulin.
  • Medication safety checks in-appEnter your current drugs and receive alerts if any are linked to menstrual changes.
  • Preparation for doctor appointmentsThe AI generates a concise report you can share, cutting average consult time by 7 minutes in user surveys.
  • Privacy and encryption by defaultAll reproductive data is stored with end-to-end encryption and never sold.

How women use Eureka’s AI doctor to manage irregular cycles privately

Women rate Eureka 4.8 out of 5 stars for period-related concerns because it combines medical expertise with around-the-clock availability. "You can request labs at 2 AM and a licensed physician reviews the order in the morning," notes Sina Hartung, MMSC-BMI.

  • Symptom triage without waiting roomsThe AI guides whether you can monitor at home, book a routine visit, or need same-day care.
  • On-demand prescriptions when appropriateIf hormonal contraception is likely beneficial and safe, the AI forwards the request to a clinician for approval.
  • Long-term tracking of treatmentsGraphing flow volume before and after therapy shows whether interventions like metformin are working.
  • Secure messaging with doctorsAsk follow-up questions and receive responses within 24 hours, keeping care continuous.
  • Free to use, no insurance barriersUsers pay nothing for core features, lowering inequities in reproductive health access.

Become your own doctor

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Frequently Asked Questions

Is it normal for my cycle to change length occasionally?

One off cycle that is a week shorter or longer can be normal, especially after stress or travel. If the pattern repeats for three cycles, seek evaluation.

Can breastfeeding cause irregular periods?

Yes. High prolactin while nursing often suppresses ovulation, leading to absent or widely spaced periods until feeds drop to about 2–3 per day.

Do irregular periods always mean infertility?

No. Many women with irregular cycles still ovulate intermittently and can become pregnant, sometimes unpredictably.

Will birth control pills fix my cycle permanently?

Pills create regular withdrawal bleeds while you take them, but the underlying cause (like PCOS) may return after stopping.

How long should I try lifestyle changes before seeing a doctor?

If cycles remain irregular after three months of tracking, stress reduction and weight stabilization, schedule a medical review.

Can vaccines or illnesses like COVID-19 disrupt periods?

Short-term changes of 1–2 cycles have been reported after infections or vaccination; they usually resolve without treatment.

What counts as a heavy period?

Needing to change a pad every hour for several hours, passing clots larger than a quarter, or bleeding longer than 8 days are heavy by clinical definition.

Should I use herbal supplements for irregular periods?

Some herbs can affect hormones, but evidence is limited and interactions exist. Discuss any supplement with your clinician before starting.

Does exercising too much stop periods?

Intense training that drops body fat below about 17 % can halt ovulation, a condition called functional hypothalamic amenorrhea.

This content is for informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for diagnosis, treatment, and personalized medical recommendations.

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