Endometriosis and Period Pain: Why It Causes Severe Dysmenorrhoea
How endometriosis causes secondary dysmenorrhoea, how to recognise it, diagnosis and NICE-recommended management.
Part of the Access Doctor period pain guide.
Key fact: Endometriosis affects approximately 1 in 10 women. The average time to diagnosis in the UK is 8 years. Severe period pain that progressively worsens over time, starts before the period, or is accompanied by pain during sex or bowel symptoms should always prompt specialist assessment. It is not “normal” to have period pain this severe.
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Start Consultation →1 in 10
women have endometriosis
8 years
average UK diagnosis delay
190M
women affected worldwide (WHO)
What Is Endometriosis?
Endometriosis is a chronic inflammatory condition in which tissue similar to the uterine lining (endometrium) grows outside the uterus. Common sites include the ovaries (where it can form “chocolate cysts” or endometriomas), the fallopian tubes, the uterosacral ligaments, the peritoneum (lining of the pelvis and abdomen), the bladder, and the bowel. Rarely, it can affect more distant sites.
Like the uterine lining, endometriosis tissue responds to monthly oestrogen and progesterone changes: it proliferates during the cycle and bleeds at menstruation. Unlike uterine tissue, it has no route of escape from the body — blood accumulates locally, causing inflammation, scarring, and adhesions over repeated cycles.
How Endometriosis Causes Period Pain
Endometriosis-related pain is more complex than primary dysmenorrhoea and involves multiple mechanisms:
- Local peritoneal inflammation — internal bleeding from lesions triggers inflammatory reactions in the surrounding tissues, producing high local concentrations of prostaglandins, cytokines, and pain-mediating molecules
- Nerve infiltration — deep infiltrating endometriosis lesions can grow into nerve fibres; nociceptive (pain) and sympathetic nerve density is increased in endometriosis tissue
- Central sensitisation — repeated cycles of pain signal the central nervous system to become increasingly sensitised; pain pathways amplify signals, meaning pain persists even when inflammation is reduced
- Adhesions — scar tissue between organs restricts movement and causes traction pain, particularly during sex, bowel movements, or bladder filling
- Ovarian endometriomas — cystic lesions on the ovaries distort ovarian architecture and cause additional inflammatory signalling
Symptoms: Distinguishing Endometriosis from Primary Dysmenorrhoea
| Feature | Primary dysmenorrhoea | Endometriosis-related dysmenorrhoea |
|---|---|---|
| Age of onset | Adolescence — within 1–2 years of first period | Any age; often worsens in 20s–30s |
| Pain progression | Stable — similar each cycle | Progressive — getting worse over months/years |
| Timing | Starts at onset of bleeding; worst day 1–2 | May begin days before the period; persists after it |
| Dyspareunia | Absent | Often present — particularly deep penetration pain |
| Bowel/bladder symptoms | Absent | Pain with defecation/urination at menstruation; dyschezia |
| Chronic pelvic pain | Absent between periods | May have non-menstrual pelvic pain |
| NSAID response | Usually good with correct timing | Partial; often insufficient at OTC doses |
Diagnosis
There is currently no reliable non-invasive blood test for endometriosis. Diagnosis options:
- Clinical assessment — specialist gynaecologist reviewing symptoms, family history, and pelvic examination; can guide empirical hormonal treatment
- Transvaginal ultrasound (TVUS) — can detect ovarian endometriomas and deep endometriosis of the rectovaginal septum; less sensitive for peritoneal disease
- MRI — better for mapping deep infiltrating endometriosis prior to surgery
- Laparoscopy — keyhole surgery; gold standard for definitive diagnosis and simultaneously allows surgical treatment (excision or ablation of lesions)
NICE NG73 recommends that women should not have surgery solely to diagnose endometriosis — empirical hormonal treatment can be initiated on clinical grounds where endometriosis is suspected.
Treatment Options per NICE NG73
| Option | Mechanism | Notes |
|---|---|---|
| NSAIDs + paracetamol | Prostaglandin suppression + central analgesia | First-line for pain relief; prescription doses needed (naproxen 500mg bd / ibuprofen 600mg tds) |
| Combined oral contraceptive pill | Suppresses ovulation and endometrial proliferation | Continuous use (no pill-free break) reduces menstrual bleeding and endometriosis activity; NOT for migraine with aura |
| Progestogen-only pill | Suppresses endometrial tissue | Useful where COC contraindicated; norethisterone, desogestrel |
| Mirena IUS (levonorgestrel) | Local progestogen — thins endometrium; reduces prostaglandins | Highly effective for pain and bleeding; does not suppress ovarian disease |
| GnRH analogues | Medical menopause — suppresses oestrogen | Highly effective; causes menopausal symptoms; time-limited; add-back HRT recommended |
| Laparoscopic surgery | Excision or ablation of lesions | For confirmed disease insufficient on medical treatment; fertility-preserving options available |
NSAIDs for Endometriosis Pain: What to Expect
NSAIDs are first-line symptomatic treatment per NICE NG73. They are less reliably effective than for primary dysmenorrhoea because the pain mechanism is more complex. Key principles:
- Use prescription doses: naproxen 500mg twice daily or ibuprofen 600mg three times daily
- Start at the first sign of pain or bleeding — do not wait
- Add paracetamol 1g for additional central analgesia
- Use heat simultaneously for additional relief
- If prescription NSAIDs provide insufficient relief, hormonal treatment should be considered alongside (not instead of) NSAIDs
When to Seek Specialist Referral
- Suspected endometriosis based on clinical features (progressive dysmenorrhoea, dyspareunia, bowel symptoms)
- Failure to respond to hormonal treatment after 3–6 months
- Ovarian endometrioma detected on ultrasound
- Difficulty conceiving with known or suspected endometriosis
- Severe symptoms significantly affecting quality of life
Emergency: Sudden severe pelvic pain in a woman with known endometriosis may indicate a ruptured endometrioma. Attend A&E.
Frequently Asked Questions
How does endometriosis cause period pain?
Endometriosis tissue bleeds internally each cycle, causing local inflammation, prostaglandin production, nerve infiltration, and central sensitisation — making pain more severe, prolonged, and complex than primary dysmenorrhoea.
What is the average time to diagnosis for endometriosis in the UK?
Approximately 8 years from symptom onset. Symptoms are often normalised or dismissed. Diagnosis requires specialist assessment; laparoscopy is the gold standard.
What symptoms distinguish endometriosis from primary dysmenorrhoea?
Progressive worsening of pain over years; pain beginning before the period and persisting after; deep dyspareunia; bowel or bladder symptoms around periods; chronic pelvic pain; poor response to NSAIDs.
Can endometriosis be managed without surgery?
Yes. Hormonal treatments (combined pill, progestogen, Mirena IUS, GnRH analogues) are effective at managing symptoms without surgery. Surgery is reserved for confirmed cases insufficient on medical treatment.
Do NSAIDs work for endometriosis period pain?
They are first-line per NICE but often less effective than for primary dysmenorrhoea. Prescription doses (naproxen 500mg twice daily; ibuprofen 600mg TDS) are needed. Where insufficient, hormonal treatment should be added.
References
- National Institute for Health and Care Excellence (NICE). Endometriosis: diagnosis and management (NG73). 2017 (updated 2024). nice.org.uk/guidance/ng73
- NHS. Endometriosis. nhs.uk/conditions/endometriosis
- Zondervan KT et al. Endometriosis. N Engl J Med. 2020;382(13):1244–1256. PubMed: 32212520
Medical disclaimer: This article is for informational purposes only. Period pain can be a symptom of an underlying condition requiring assessment. In an emergency call 999.