Iberogast (STW5 herbal blend)

Iberogast, known in the research literature as STW 5, is a German liquid preparation of nine plant extracts, including bitter candytuft, chamomile, peppermint, caraway, liquorice, lemon balm, angelica, milk thistle, and greater celandine. It has been used in Germany for decades and is marketed in several countries as a licensed herbal medicine for functional dyspepsia and IBS; in the United States it is sold as a dietary supplement. Laboratory work attributes to it a mix of effects on gut muscle tone, acid secretion, and sensitivity in different regions of the gut PMID 23263639.

The IBS evidence is one trial. A double-blind, multicentre study randomised 208 patients with IBS, after a standardised diagnostic work-up, to four arms for four weeks: the commercial STW 5 (51 patients), a six-herb research version STW 5-II (52), bitter candytuft extract alone (53), or placebo (52). Both multi-herb preparations reduced the total abdominal pain score and the IBS symptom score more than placebo on intention-to-treat analysis (p = 0.0009 and p = 0.001 for STW 5), while candytuft alone did not differ from placebo; 203 patients completed the trial PMID 14984373. A 2013 review summarising 12 clinical trials of STW 5 in functional dyspepsia and IBS since 1990 reported statistically significant effects over placebo and an adverse drug reaction rate of 0.04% in trials, though most of that evidence concerns dyspepsia rather than IBS, and the review’s authors include people with industry links PMID 23263639.

The safety picture has changed since those trials. Published case reports describe acute liver injury attributed to Iberogast: a German report of acute liver failure in which re-exposure and an in-vitro assay supported causality PMID 31246695, and a Swiss case of severe acute hepatitis in a 32-year-old with no prior illness that resolved five weeks after stopping the product PMID 39132058. The ingredient most often implicated is greater celandine (Chelidonium majus), which has its own record of liver toxicity in herbal medicine. These cases are rare against the product’s wide use, but they mean the “safe herbal” framing deserves qualification, and the product information in some markets now carries a liver warning.

Points clinicians commonly raise: the IBS trial was four weeks long, so nothing is known about longer-term efficacy in IBS specifically; the dyspepsia evidence does not transfer automatically to lower-gut symptoms; anyone with existing liver disease, or taking other medicines that can affect the liver, should ask before using it; and symptoms such as jaundice, dark urine, or pale stools while taking it warrant stopping and seeking care promptly.

Talk to a clinician before starting or stopping anything.