Spearmint leaf (Mentha spicata) has a long history of traditional use for various digestive complaints, including indigestion, flatulence, and gastrointestinal discomfort. In the context of Irritable Bowel Syndrome (IBS), however, most of the robust clinical evidence pertains to peppermint oil (Mentha piperita), which contains higher concentrations of menthol and has demonstrated efficacy in several randomized controlled trials for reducing abdominal pain and improving overall IBS symptoms. Spearmint leaf contains similar, but generally lower, levels of volatile oils, including carvone and limonene, which are believed to have antispasmodic and carminative effects that could theoretically benefit IBS sufferers by relaxing gastrointestinal smooth muscle and reducing gas.

Scientific evidence specifically evaluating spearmint leaf (as opposed to peppermint oil) for IBS is limited. A few small studies and animal experiments suggest that spearmint extracts may have mild anti-inflammatory and antispasmodic properties, but these findings are preliminary and not directly focused on IBS populations. No large-scale, high-quality human trials have confirmed a clear benefit of spearmint leaf for IBS. Therefore, while there is a plausible mechanism and weak preliminary data, the overall quality and quantity of evidence is low, and its use for IBS is primarily extrapolated from related traditional uses and from evidence for peppermint rather than from direct clinical research on spearmint itself.