Rome V vs Rome IV: what actually changed in 2026.

Every six to ten years, the Rome Foundation, the international body of gastroenterologists who define and classify what used to be called functional GI disorders, publishes an update. The 2026 release is Rome V. It is the most consequential revision since Rome III in 2006.

If you have been told you have IBS, functional dyspepsia, cyclic vomiting, or any of the conditions that live in the gut-brain space, what changed in Rome V probably affects how your condition is named, diagnosed, and treated. Here is the short version.

The name changed for a reason

Rome IV used 'functional GI disorders' as the umbrella term. The word functional meant nothing was wrong with the structure of the gut. In practice, patients heard it as 'we cannot find anything,' which is not the same thing.

Rome V retired the word functional and adopted disorders of gut-brain interaction (DGBI) as the umbrella. The change is not cosmetic. It reflects a decade of neuroimaging, motility, and microbiome research showing that DGBI involve real, measurable abnormalities in how the gut and brain talk to each other. The biology is there. The tests just are not in clinic yet.

Prevalence numbers moved

Rome V revised the global prevalence of DGBI from roughly 40 percent to 42.2 percent. That sounds small until you look at the specific conditions.

• IBS prevalence roughly doubled, from around 4.1 percent in Rome IV to 8.9 percent in Rome V. The methodology was tightened, but the underlying signal also grew.
• Cannabinoid hyperemesis syndrome (CHS) increased roughly 12-fold, from 0.05 percent to 0.6 percent of adults. Most of this is real-world growth tied to expanded cannabis access.
• Functional dyspepsia held roughly steady at 7 to 8 percent depending on country.
• Unspecified bowel disorder (U-BD), a newer Rome V category, captures a transitional population of about 60 percent of people who do not yet meet full IBS criteria but will within two years.

New conditions added

Rome V added abdominal migraine to the adult criteria. Previously it was a pediatric-only category. Most adults with episodic abdominal pain plus migraine features were getting cycled through IBS workups that never quite fit. They have a name now.

CHS got its own formal criteria (B2c) requiring at least four episodes per week, at least one year of regular cannabis use, and at least six months of symptom resolution with abstinence. Before Rome V, CHS was a clinical impression. Now it has a definition.

Central sensitization is the new throughline

Rome IV used the term central sensitization in passing. Rome V puts it in the title of an entire chapter and uses it as the explanatory mechanism for why IBS, fibromyalgia, migraine, chronic fatigue, and a chunk of dyspepsia symptoms travel together. The same nerves carry pain and fullness signals. When those nerves get turned up over months and years, ordinary inputs feel louder than they should. That is the cluster.

If you have IBS plus migraines plus fatigue plus brain fog, that combination is no longer four separate diagnoses. Rome V treats it as one wiring problem expressing in four tissues.

Clinical Criteria vs Research Criteria

Rome V split each condition's criteria into two tiers. Clinical Criteria are looser, designed for use in a real exam room with a real patient who almost meets the rule. Research Criteria are stricter, designed for trials. The split acknowledges what every clinician already knew: the strict Rome IV criteria were excluding people who clearly had the condition. Clinical Criteria let those people get treated.

Treatments that moved up the ladder

Rome V published more affirmative nutraceutical guidance than any prior edition. Glutamine and palmitoylethanolamide (PEA) got endorsed for IBS. The chapter on central sensitization explicitly endorses digital biomarker tracking (think MeNome) as a Level 2 recommendation. Low-dose tricyclics, gut-directed hypnotherapy, and CBT are reaffirmed.

Magnesium gets mentioned as an osmotic laxative for constipation, but Rome V is silent on magnesium glycinate's role in central sensitization (a gap our formulation thesis fills). Allithiamine (lipid-soluble vitamin B1) is also not addressed, which is whitespace for clinical research, not a refutation.

What to do

1. If you have a DGBI diagnosis from before 2026, ask your clinician at your next visit whether the Rome V criteria change how they would frame your condition.
2. If your symptom cluster includes migraine, fatigue, fibromyalgia, or brain fog plus gut issues, ask specifically about central sensitization rather than running them as separate workups.
3. If you have a long history of cannabis use plus cyclic vomiting, the CHS criteria are now formal. A clinician can diagnose it.
4. Use the BellyMD Learn library for plain-language summaries. Every condition page is mapped to its Rome V chapter.