Endometriosis or IBS? How to tell the overlap apart

SASian Anderson, Writer and editor, MyGLP. Sources checked 5 November 2026.

Why the two get mixed up

Irritable bowel syndrome is a common, long-term gut condition. The NHS IBS page lists the main symptoms as tummy pain or cramping which often eases after a poo, bloating, diarrhoea and constipation. Symptoms come and go in flare-ups. There is no specific test for IBS, so it is diagnosed from your symptoms once other conditions have been ruled out.

Endometriosis can sit on or near the bowel. The NHS endometriosis page says diagnosis can take a long time because its symptoms overlap with other conditions, and names IBS as one of them. Endometriosis UK says bowel endometriosis symptoms are similar to IBS and can vary with the menstrual cycle, getting worse in the days before and during a period.

In a 2024 survey of 4,371 people by Endometriosis UK, the average wait for an endometriosis diagnosis was 8 years and 10 months. An IBS diagnosis can be correct and still leave endometriosis unlooked for. Neither condition rules the other out.

You can have both

A 2022 systematic review and meta-analysis by Nabi and colleagues pooled studies on the two conditions. Women with endometriosis had about three times the odds of IBS (odds ratio 2.97). Across the studies, 23.4% of women with endometriosis also met the criteria for IBS, with individual studies ranging from 10.6% to 52%. A confirmed IBS diagnosis does not close the endometriosis question, and the reverse is true too.

Symptoms side by side

The cyclical clue

The NICE endometriosis guideline, NG73, tells clinicians to suspect endometriosis in women with period-related or cyclical gut symptoms, in particular painful bowel movements. It also lists period-related urinary symptoms, chronic pelvic pain, period pain affecting daily life, deep pain with sex, and fertility problems alongside any of these. The word that matters is cyclical. IBS flares are linked to food, stress and other triggers. A pattern tied to your cycle points the conversation towards endometriosis.

What to track

NICE says a symptom diary can aid discussions about endometriosis. Two months gives a clear picture. Each day, note:

• Your cycle day, with day 1 as the first day of bleeding.
• Tummy pain, bloating and pain when pooing, each scored 0 to 10.
• Bowel habit: loose, normal, hard, or none.
• Pain when peeing, and any blood in your urine or from your bottom.
• Pain during or after sex.
• Foods, alcohol and stress you think set off a flare.
• If you take a weight loss medicine, your injection or tablet day and any dose change.

Lay the two months side by side. Pain which peaks in the same cycle days each month is the pattern to show your GP.

Tests to ask for

Your GP will decide which tests suit you, but these are the guideline points worth knowing.

1. A coeliac blood test. NICE quality standard QS134 says adults who meet the criteria for IBS should be offered one. The test is only accurate if you have eaten gluten for at least 6 weeks before it.
2. A transvaginal ultrasound if endometriosis is suspected. NG73 says to offer one to everyone with suspected endometriosis, and a normal scan does not rule it out.
3. A CA125 blood test if you are 50 or over. NICE quality standard QS18 says women of 50 or over with persistent or frequent bloating, early fullness, pelvic or tummy pain, urinary urgency, or symptoms suggesting IBS should be offered CA125, a test linked to ovarian cancer. Women under 50 can be offered it where clinically appropriate.
4. Referral to gynaecology if symptoms persist despite treatment or affect daily life, as NG73 sets out.

What to say at the appointment

Open with the pattern. "My bowel symptoms get worse around my period, and here are two months of notes." Then ask the direct question: "Could this be endometriosis as well as, or instead of, IBS?" If you already have an IBS diagnosis, you can ask for it to be reviewed in light of the cyclical pattern. You can also ask to see a GP with an interest in women's health. Our guide to getting heard at the GP covers longer appointments and second opinions.

The Women's Health Strategy for England (2022) recorded that 84% of women who responded to its call for evidence said a health professional had not listened to them at some point, with particular concern where pain is the main symptom. This is about systems catching up with the evidence. Bringing a diary makes the evidence hard to miss.

Weight loss medicines muddy the picture

The NHS tirzepatide page lists nausea, vomiting, constipation, diarrhoea and stomach pain among the common side effects of Mounjaro. Those overlap with IBS and with bowel endometriosis. Three steps keep the picture clear:

• Log your dose days in the same diary as your cycle. A pattern which follows the dose rather than the cycle is worth raising with your prescriber.
• Tell your GP the date you started and the date of each dose rise.
• Do not put new bowel symptoms down to the jab without checking. Rectal bleeding, weight loss you cannot explain and a lump in the tummy need a GP, whatever medicine you take.

Constipation on a jab has its own fixes, which our fibre and constipation guide covers.

For the full picture on endometriosis, including treatment and fertility, see our endometriosis guide. For pain that centres on your period, see period pain: when to get help.

Sources

1. Irritable bowel syndrome (IBS) (NHS)
2. Endometriosis (NHS)
3. Endometriosis and the bowel (Endometriosis UK)
4. Endometriosis and irritable bowel syndrome: a systematic review and meta-analyses (Nabi et al, 2022)
5. Endometriosis: diagnosis and management (NG73), recommendations (NICE)
6. Coeliac disease quality standard (QS134), statement 1 (NICE)
7. Ovarian cancer quality standard (QS18), statement 1: symptoms and CA125 (NICE)
8. Dismissed, ignored and belittled: diagnosis survey, March 2024 (Endometriosis UK)
9. Women's Health Strategy for England (2022) (Department of Health and Social Care)
10. Tirzepatide (NHS)