Periods
A clinically reviewed guide to period delay, heavy periods, painful periods, irregular periods and missed periods — causes, treatment options and when to seek help. NICE-aligned. Not a guide to contraception.
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Periods UK: A Complete Guide to Menstrual Health
A clinically reviewed guide covering period delay, heavy periods, painful periods, irregular periods and missed periods — causes, treatment options, and when to seek help. Aligned to NICE guidance.
Periods are a normal part of life for most women between puberty and the menopause — but they are not always straightforward. This guide covers five of the most common period-related concerns: delaying your period for a holiday or event, heavy periods (menorrhagia), painful periods (dysmenorrhoea), irregular periods, and missed periods. For each, we cover what causes it, what treatment options exist, and when it warrants medical attention. This guide does not cover contraception.
What Is a Normal Period?
Menstruation — commonly called a period — is the monthly shedding of the uterine lining when a pregnancy has not occurred. Most women have their first period between the ages of 11 and 16 and continue until the menopause, which in the UK occurs at an average age of 51.
A normal period typically:
- Lasts between 2 and 7 days
- Occurs every 21 to 35 days (28 days on average)
- Involves 30–80ml of blood loss per cycle (roughly 3–6 tablespoons)
- May be accompanied by mild cramping, particularly on the first day or two
There is significant natural variation between women, and a period that differs from these averages is not necessarily abnormal — what matters is whether it has changed from what is normal for you.
How the Menstrual Cycle Works
Understanding the menstrual cycle helps explain why periods can be delayed, become heavy or painful, or stop altogether.
Days 1–5: Menstruation
Progesterone and oestrogen fall. The uterine lining sheds as your period. Prostaglandins trigger uterine contractions, which cause cramping.
Days 1–13: Follicular phase
FSH stimulates follicles in the ovaries to develop. Oestrogen rises, rebuilding the uterine lining.
Day ~14: Ovulation
A surge in LH triggers ovulation. The dominant follicle releases an egg. This is when conception can occur.
Days 15–28: Luteal phase
Progesterone rises to maintain the uterine lining. If no fertilised egg implants, progesterone falls — triggering the next period.
Period delay tablets work by maintaining progesterone levels artificially during the luteal phase, preventing the lining from shedding. Heavy and painful periods are influenced by the degree of uterine contraction and the volume of lining built up. Irregular or missed periods usually indicate a disruption somewhere in this hormonal cycle.
Period Delay
Delaying a period is safe and common — most often for a holiday, a sporting event, a wedding, or another occasion where a period would be inconvenient or distressing. There are two approaches, depending on whether you are on the combined pill or not.
Norethisterone 5mg (for women not on the pill)
Norethisterone is a synthetic progestogen that artificially maintains progesterone levels, preventing the uterine lining from shedding. It is the standard prescription option for women who are not taking hormonal contraception and want to delay their period.
| Detail | Norethisterone 5mg |
|---|---|
| When to start | 3 days before expected period |
| Dose | One 5mg tablet three times daily |
| Maximum duration | Up to 20 days (giving up to 17 days of delay) |
| When period returns | 2–3 days after stopping (occasionally up to a week) |
| Is it a contraceptive? | No. Continue using your usual contraception |
| Availability | Prescription only. Available online via Access Doctor |
Important: Norethisterone must be started at least 3 days before your expected period. Once bleeding has begun, it cannot stop it. Plan ahead and allow enough time to order and receive your tablets before your event.
Combined pill (for women already on hormonal contraception)
If you already take a combined oral contraceptive pill, you can delay your period by running packs back-to-back, skipping the usual 7-day pill-free interval. This is a well-established, safe approach recommended by FSRH guidelines. It falls under the management of your existing contraception and does not require a separate prescription in most cases — speak to your prescriber or GP for guidance.
This guide does not cover contraception in detail. Norethisterone for period delay is entirely separate from contraceptive use.
Who cannot use norethisterone for period delay
- Women with a personal history of blood clots (DVT or pulmonary embolism)
- Active or recent liver disease
- Hormone-sensitive cancers (including certain breast cancers)
- Pregnancy
- Unexplained vaginal bleeding (cause should be investigated first)
Period Delay Prescription
Access Doctor's GPhC-registered pharmacist independent prescribers can assess your suitability for norethisterone online. No GP appointment needed. Discreet next-day delivery.
View Period Delay Treatment →Heavy Periods (Menorrhagia)
Heavy periods — medically termed menorrhagia — are defined as blood loss exceeding 80ml per cycle (roughly 6 tablespoons), though in clinical practice the impact on quality of life matters more than the volume. If your periods are soaking through pads or tampons within an hour, passing large clots, or leaving you exhausted or anaemic, they are clinically heavy.
What causes heavy periods?
Fibroids
Non-cancerous growths in or around the uterus. One of the most common identifiable causes of heavy periods. Size and position determine how much they affect bleeding.
Adenomyosis
Uterine lining tissue grows into the muscular wall of the uterus. Causes heavy, painful periods and a bulky uterus. Often underdiagnosed.
Endometriosis
Uterine lining tissue grows outside the uterus. Associated with heavy, painful periods and pelvic pain. Requires specialist assessment.
Thyroid disorders
Both underactive (hypothyroidism) and overactive (hyperthyroidism) thyroid conditions can disrupt menstrual bleeding. A simple blood test can identify this.
PCOS
Polycystic ovary syndrome disrupts ovulation, leading to irregular cycles and sometimes heavy periods when they do occur.
No identifiable cause
In many women, no structural or hormonal cause is found (dysfunctional uterine bleeding). Treatment focuses on managing blood loss.
Treatment options for heavy periods
| Treatment | How it works | NICE position |
|---|---|---|
| Tranexamic acid | Reduces blood loss by preventing the breakdown of blood clots in the uterus. Non-hormonal. Taken during the period only. | First-line for women who do not want hormonal treatment |
| Mefenamic acid | NSAID that reduces prostaglandin production — reduces both bleeding and period pain. Taken during the period only. | First-line, especially if period pain is also present |
| Norethisterone (higher dose) | Taken from day 5 to day 26 of the cycle to reduce blood loss. Different dose and schedule from period delay use. | Second-line when first-line options insufficient |
| Combined pill or hormonal IUS | Hormonal treatments that significantly reduce menstrual blood loss over time. Covered under contraception guidance. | Highly effective — discuss with GP or prescriber |
Iron deficiency anaemia is a common consequence of heavy periods. If you feel persistently tired, short of breath, or have a fast heartbeat alongside heavy bleeding, ask your GP about a blood test and whether iron supplementation is needed.
Painful Periods (Dysmenorrhoea)
Period pain — medically called dysmenorrhoea — is one of the most common gynaecological conditions. It affects up to 80% of women at some point and is the leading cause of short-term school and work absence in young women in the UK.
Primary vs secondary dysmenorrhoea
| Primary dysmenorrhoea | Secondary dysmenorrhoea | |
|---|---|---|
| Definition | Period pain with no identifiable underlying cause | Period pain caused by an underlying condition |
| When it starts | Usually begins shortly after periods start | Often develops later in reproductive years |
| Typical timing | First 1–3 days of period | May begin before period and persist through it |
| Associated with | Prostaglandin overproduction causing uterine spasm | Endometriosis, fibroids, adenomyosis, pelvic inflammatory disease |
| First-line treatment | NSAIDs (ibuprofen, mefenamic acid), heat | Treat the underlying condition; specialist referral may be needed |
Treatment options for painful periods
- NSAIDs — ibuprofen (400–600mg three times daily) or mefenamic acid (500mg three times daily) started at the onset of pain or bleeding. More effective when started before pain becomes severe. NICE first-line for primary dysmenorrhoea.
- Heat — a heat pad or hot water bottle on the lower abdomen provides meaningful pain relief and is supported by clinical evidence alongside medication.
- Mefenamic acid — available on prescription; reduces both prostaglandin production (pain) and blood loss (helpful if heavy periods also present).
- Transcutaneous electrical nerve stimulation (TENS) — a non-drug option that can reduce pain perception for primary dysmenorrhoea.
When period pain needs investigation: Pain that is worsening over time, present outside of periods, associated with deep pain during sex, or not responding to standard treatment warrants investigation for endometriosis, adenomyosis, or other underlying conditions. See your GP.
Irregular Periods
Periods are considered irregular when the cycle length varies by more than 7–9 days from cycle to cycle, or when cycles are consistently shorter than 21 days or longer than 35 days. Occasional irregularity is common and not usually cause for concern. Persistent irregularity warrants investigation.
Common causes of irregular periods
- Polycystic ovary syndrome (PCOS) — one of the most common causes of irregular or absent periods in women of reproductive age. PCOS disrupts ovulation, leading to infrequent, unpredictable cycles.
- Thyroid disorders — both hypothyroidism and hyperthyroidism can significantly disrupt the menstrual cycle. A blood test (TSH) is a simple first investigation.
- Significant weight change — substantial weight loss or gain disrupts the hormonal signalling needed for regular ovulation.
- Excessive exercise or low body weight — hypothalamic amenorrhoea, where the body suppresses reproductive function in response to low energy availability.
- Stress — chronic psychological or physical stress can disrupt the hypothalamic-pituitary-ovarian axis and delay or suppress ovulation.
- Perimenopause — in women approaching menopause (typically from the mid-40s), cycles naturally become more irregular before stopping.
- Certain medications — including antipsychotics, antidepressants, and some antiepileptics.
Investigating irregular periods: Your GP will typically start with a blood test panel including LH, FSH, prolactin, TSH, and testosterone, alongside a pelvic ultrasound if PCOS is suspected. Treatment depends entirely on the underlying cause.
Missed Period
A missed period — or amenorrhoea — has a wide range of causes. The approach depends entirely on context.
If you have missed one period
A single missed period in a woman with an otherwise regular cycle is most commonly caused by:
- Pregnancy — always the first thing to rule out with a home pregnancy test
- A period of unusual stress, illness, or disrupted sleep
- Significant changes in exercise, diet, or body weight
- A late or delayed ovulation in that particular cycle
If you have missed three or more periods (secondary amenorrhoea)
Missing three or more consecutive periods in a woman who has previously had regular cycles — and who is not pregnant — warrants investigation. Common causes include:
- PCOS — by far the most common cause in women of reproductive age
- Thyroid disorders — both over- and underactive thyroid
- Hyperprolactinaemia — elevated prolactin (a pituitary hormone) suppresses ovulation
- Hypothalamic amenorrhoea — caused by excessive exercise, very low body weight, or eating disorders
- Premature ovarian insufficiency (POI) — early menopause occurring before age 40
See your GP if you have missed three or more periods and a pregnancy test is negative. This always warrants a blood test to investigate the cause. Do not ignore prolonged absent periods — even if you are not trying to conceive, the underlying cause may need treatment.
When to See a Doctor About Your Periods
Most period changes are benign and manageable, but the following warrant prompt medical assessment:
- Periods that have recently become significantly heavier, more painful, or irregular without an obvious cause
- Bleeding between periods or after sex
- Period pain that is worsening over time or present outside of your period
- Pelvic pain unrelated to your period
- Periods that have stopped for 3 months or more (and pregnancy is excluded)
- Symptoms of anaemia alongside heavy bleeding (fatigue, breathlessness, fast heartbeat)
- Pain during sex alongside period problems
Seek urgent medical attention if you experience sudden, severe pelvic pain, heavy bleeding with signs of haemodynamic compromise (dizziness, feeling faint, rapid heartbeat), or fever alongside abnormal bleeding. Call 999 or attend A&E.
Access Doctor — Women’s Health Prescriptions
Access Doctor's GPhC-registered pharmacist independent prescribers can assess your suitability for period-related treatments including norethisterone for period delay and medications for heavy or painful periods. No GP appointment needed.
View Women’s Health Treatments →All Period Health Guides
Clinically reviewed guides covering period delay, norethisterone and period management — authored by Dr Abdishakur M Ali, GMC no. 7041056.
Frequently Asked Questions
Can you delay your period safely?
Yes. Norethisterone 5mg is a prescription tablet that delays your period for up to 17 days. It is taken three times daily starting 3 days before your expected period. It is safe for most healthy women when used short-term under clinical guidance, and is not a contraceptive. Women already on the combined pill can also delay their period by running packs back-to-back — this falls under contraception management rather than period delay treatment.
What causes heavy periods?
Heavy periods (menorrhagia) affect around 1 in 3 women at some point. Common causes include fibroids, adenomyosis, endometriosis, PCOS, thyroid disorders, and blood clotting conditions. In many cases no specific cause is found (dysfunctional uterine bleeding). Treatment options range from tranexamic acid and mefenamic acid to hormonal management.
What causes painful periods?
Painful periods (dysmenorrhoea) are caused by prostaglandins — hormone-like substances that trigger uterine contractions. Primary dysmenorrhoea has no underlying cause; secondary dysmenorrhoea is caused by conditions such as endometriosis, fibroids, or adenomyosis. NSAIDs such as ibuprofen and mefenamic acid are first-line treatment.
What causes irregular periods?
Common causes include PCOS, thyroid disorders, significant weight changes, stress, excessive exercise, and perimenopause. Investigating the underlying cause is important before starting treatment.
What causes a missed period?
The most common cause is pregnancy — always do a pregnancy test first. Other causes include PCOS, thyroid disorders, stress, low body weight, and perimenopause.
What is the difference between norethisterone for period delay and for heavy periods?
Norethisterone is used at different doses for different purposes. For period delay: 5mg three times daily starting 3 days before expected period — not a contraceptive at this dose. For heavy periods: higher doses from day 5 to day 26 of the cycle to reduce blood loss. Both require a prescription and clinical assessment.
When should I see a GP about my periods?
See a GP or prescriber if: your periods have recently become significantly heavier, more painful, or irregular; you have bleeding between periods or after sex; you have pelvic pain outside of your period; you have missed three or more periods without a clear cause; or your period symptoms are significantly affecting your quality of life.
References
- NICE. Heavy menstrual bleeding: assessment and management (NG88). Updated 2021. nice.org.uk/guidance/ng88
- NICE. Dysmenorrhoea: CKS. Updated 2023. cks.nice.org.uk
- NICE. Irregular vaginal bleeding: CKS. Updated 2023. cks.nice.org.uk
- MHRA. SPC: Norethisterone 5mg tablets. medicines.org.uk/emc
- NHS. Periods. nhs.uk/conditions/periods
- NHS. Heavy periods. nhs.uk/conditions/heavy-periods
- NHS. Period pain. nhs.uk/conditions/period-pain
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. The treatments discussed are prescription-only medicines — a clinical consultation is required before they can be dispensed. This guide does not cover contraception. In a medical emergency, call 999.
