A number of probiotic strains have been shown to reduce abdominal pain, bloating, and intestinal transit time while improving stool consistency. However, the effects appear to be temporary, with most benefits seen around six to eight weeks of supplementation even though some participants continued to take the probiotics for twelve weeks.[1][2]
Doctors might also recommend over-the-counter fiber supplements if increasing dietary fiber doesn't help. Psyllium husk appears to be effective for normalizing stool in both IBS-C and IBS-D.[3] Additionally, peppermint oil can ease IBS-associated abdominal pain.[4]
One study found that a traditional Persian blend of herbal extracts had a laxative effect greater than placebo; interestingly, the British Pharmacopoeia simple syrup used to compound the blend, which served as placebo, itself also had a noticeable laxative effect.[5] This could be due to the high concentration of sugar causing water retention in the intestine and easing stool transit.
Flixweed (Descurainia sophia), a common weed also known as tansy mustard, was as effective as figs for improving pain, distension, and bowel movement frequency.[6]