Efficacy and safety of "Yahom" as a traditional Thai herbal therapy: A systematic review

Ethnopharmacological relevance: Yahom is a traditional Thai medicine used to treat syncope and abdominal discomfort.

Aim of the study: This study aimed to systematically review all available evidence which purports to support these claims.

Material and methods: The systematic review accorded with the Cochrane Collaboration framework and PRISMA reporting. Databases including MEDLINE, Excerpta Medica Database (EMBASE), Cochrane library database, and Google Scholar were searched by keywords, Yahom and Ya-hom. Pharmacological and toxicity data from non-animal and animal studies were included.

Results: Twenty-four articles: 2 on in vitro cell lines or bacteria, 3 in vitro cell-free, 5 in vitro animal, 13 in vivo and 1 human mainly reported (A) Cardiovascular effects (i) transient hypotension (0.2-0.8g/kg, intravenous injection (i.v.)), increased cerebral blood flow (2g/kg, single oral) and vascular dilatation/relaxation (ii) elevated blood pressure (BP) (0.2-0.8g/kg, i.v. or 2-4g/kg oral) and vasocontraction. Single Yahom doses (3g) given to healthy volunteers had no effect on cutaneous blood flow, ECG or systolic BP although marginally increased diastolic BP was claimed. (B) Yahom (2-4g/kg) completely inhibited gastric acid secretion evoked by gastric secretagogues. (C) Toxicity: Chronic oral doses of selected Yahoms to rodents (0.001-1g/kg) supports its status as generally regarded as safe.

Conclusions: Most studies supported declared objectives relating to perceived Yahom actions, but lacked background demonstrating clinical efficacy, and mechanistic data that would validate conclusions. Our study suggests that research into traditional medicinal herbs needs underpinning by appropriate clinical interventions and pharmacovigilance, thereby optimising efficacy and minimizing toxicity by combining traditional wisdom and modern testing.