Irregular periods
A normal menstrual cycle lasts between 21 and 35 days, and a period lasts 2 to 7 days. Periods are considered irregular when the cycle length varies by more…
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Medicines commonly prescribed for Irregular periods
For informational purposes only. Always consult a doctor before taking any medication.
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Irregular periods
A normal menstrual cycle lasts between 21 and 35 days, and a period lasts 2 to 7 days. Periods are considered irregular when the cycle length varies by more than 7–9 days from one month to the next, when months are skipped, or when periods come too frequently. Occasional irregularity is normal; what deserves investigation is a sustained pattern, because there is nearly always an identifiable and treatable cause.
What counts as irregular
- cycles shorter than 21 days or longer than 35;
- a difference of more than 7–9 days between consecutive cycles;
- no period for three months or more, without pregnancy;
- bleeding between periods;
- very heavy periods or periods lasting more than 7 days;
- bleeding after sex;
- any bleeding after the menopause: this must always be assessed.
When irregularity is expected
- in the first two to three years after the first period;
- in the perimenopause, from around 40–45;
- after childbirth and during breastfeeding;
- in the first months after stopping hormonal contraception;
- with hormonal devices and methods, depending on the type.
Causes
- polycystic ovary syndrome: the commonest cause in the reproductive years; it comes with acne, excess hair and sometimes excess weight;
- thyroid disorders, both over- and underactive;
- raised prolactin, with or without nipple discharge;
- severe stress, which suppresses ovulation;
- significant weight loss, low body weight or eating disorders;
- very intensive exercise, common in athletes;
- excess weight;
- fibroids and uterine polyps: more associated with heavy or intermenstrual bleeding;
- endometriosis and adenomyosis;
- premature ovarian insufficiency, if it occurs before 40;
- medicines: anticoagulants, antipsychotics, antidepressants, corticosteroids, chemotherapy;
- chronic conditions: coeliac disease, poorly controlled diabetes, kidney or liver disease;
- pregnancy, including ectopic pregnancy, which must always be excluded first.
When to see a doctor
- your cycles have been irregular for several months;
- you have had no period for three months and are not pregnant;
- there is bleeding between periods or after sex;
- periods are so heavy that you change a pad or tampon every 1–2 hours, or pass large clots;
- there is severe pelvic pain;
- you are unable to conceive;
- there is increased facial hair, severe acne or hair loss;
- there is nipple discharge;
- you have gained or lost a significant amount of weight;
- you have hot flushes and are under 45;
- there is marked tiredness or pallor: anaemia is possible;
- any bleeding after the menopause.
Urgent care: very heavy bleeding with dizziness, pallor or fainting, or severe abdominal pain with a missed period, because of the possibility of an ectopic pregnancy.
Consult with a doctor about Irregular periods
Discuss your symptoms and possible next steps with a doctor online.
How it is investigated
- a pregnancy test, always first;
- full blood count and ferritin, to assess anaemia;
- thyroid function and prolactin;
- FSH, LH, oestradiol and androgens, in the first days of the cycle;
- glucose and insulin if polycystic ovary syndrome is suspected;
- gynaecological ultrasound;
- cervical screening according to your programme;
- endometrial biopsy in women with risk factors or postmenopausal bleeding;
- clotting studies if heavy bleeding has been present since adolescence.
The most useful thing to bring: a record of the last three to six months with the start and end dates of each period and an estimate of the flow. A phone app is perfectly adequate.
Treatment
- treat the cause: this is what resolves the problem — thyroid, prolactin, weight, polycystic ovary syndrome;
- hormonal contraception to regulate the cycle and reduce bleeding;
- hormonal intrauterine device: very effective for heavy periods;
- cyclical progestogens where there is no ovulation;
- tranexamic acid and anti-inflammatories to reduce bleeding during the period;
- iron if there is anaemia or low ferritin;
- metformin in polycystic ovary syndrome with insulin resistance;
- ovulation induction if you are trying to conceive;
- surgery for fibroids and polyps where warranted.
What you can do
- keep a record of your cycles;
- maintain a stable weight and avoid extreme diets;
- adjust your training load if it is very high;
- sleep well and manage stress: they affect ovulation more than people expect;
- eat enough iron and protein;
- do not smoke;
- use contraception if you do not want to conceive: an irregular cycle is not protective;
- review your medicines with your doctor.
Common questions
Can I get pregnant with irregular cycles? Yes. Ovulation is unpredictable, not absent.
Is it normal to skip a period occasionally? A single episode can follow stress or illness. If it repeats, it should be investigated.
Do contraceptives "fix" the cycle? They create a regular withdrawal bleed but do not correct the cause. The previous pattern returns when you stop.
Does irregularity affect fertility? It can make conceiving harder, particularly without ovulation. It is treatable.
Should I worry in adolescence? The first few years are usually irregular. It is worth attending if the first period has not arrived by 15–16.
Online consultation
In an online consultation the doctor reviews your cycle record, excludes pregnancy, directs the assessment towards the most likely cause, advises which tests to have and on which day of the cycle, and explains the treatment options depending on whether or not you are trying to conceive.
This material is for information only and does not replace a medical consultation.
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Reviewed on Jul 12, 2026
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