Curcumin (turmeric)

Curcumin is the yellow polyphenol in turmeric root, sold as a supplement at doses far above what cooking provides and often formulated with piperine or lipids to improve its poor absorption. The rationale in IBS rests on anti-inflammatory and antioxidant effects seen in laboratory and animal models of colitis, and on possible effects on gut bacteria PMID 30248988. Products vary widely: some contain purified curcumin, some whole turmeric or Curcuma xanthorrhiza extracts, and some combine curcumin with other herbal ingredients, which makes trial results hard to compare.

The only meta-analysis, published in 2018, screened trials from 1988 to 2018, reviewed five randomised controlled trials, and could pool three of them, covering 326 patients. The pooled standardised mean difference in IBS severity was -0.466 in favour of curcumin, with a confidence interval from -1.113 to 0.182 and a p-value of 0.158, so the trend did not reach statistical significance. No adverse events were reported in the included trials, and the authors described the evidence base as limited with marked heterogeneity, calling for larger trials with a standardised preparation PMID 30248988.

The individual trials illustrate the problem. An Italian multicentre trial randomised 121 patients with mild-to-moderate IBS to a combination of curcumin and fennel essential oil or placebo for 30 days; the relative fall in severity score was 50.1% versus 26.1%, and 25.9% of the active group were symptom-free at the end versus 6.8% on placebo PMID 27308645. Because fennel oil has its own antispasmodic rationale, the trial cannot say what curcumin contributed on its own. By contrast, a German double-blind trial gave 106 patients Curcuma xanthorrhiza 60 mg daily, fumitory, or placebo for 18 weeks, and found no difference in pain, distension, global symptom change, or stress on any comparison; the authors concluded that neither herb could be recommended PMID 16173134.

Points clinicians commonly raise: the positive signal comes from combination products and short trials, while the longest placebo-controlled trial of a curcuma extract was negative; doses in the trials differ by orders of magnitude, so a result with one product does not transfer to another; turmeric as a food spice is a different matter from concentrated extracts; and curcumin supplements have been associated with interactions and, rarely, liver abnormalities in reports outside IBS, so anyone on regular medication should check before adding one.

Talk to a clinician before starting or stopping anything.