Rang Chuet (Thunbergia laurifolia Lindl.) is a Thai medicinal plant with pharmacological properties: it can be used as an antidote, for decreasing body temperature and it is addictive. This study investigated total phenolic contents and antioxidant activities of Rang Chuet extracts, and its acute and sub-chronic toxicities of Rang Chuet extracts. To investigate the acute toxicity of Rang Chuet, male and female Wistar rats were orally gavaged with a single dose of 2,000 and 15,000 mg/kg body weight of Rang Chuet leaf extracts prepared by three different extraction solvents, namely water, ethanol, and acetone. The Rang Chuet water extract showed the highest total phenolic contents at 2,643±195.05 mg GAE/ 100 g while the Rang Chuet acetone extract showed the lowest IC50 at 52.91 mg/ml by DPPH assay. The sub-chronic toxicity study was performed using Wistar rats of both sexes which were gavaged with ethanol and water Rang Chuet extracts for 90 days. Rats were gavaged with the equivalent dose of Rang Chuet in a typical consumer drink (to be taken 3 times a day, at dose 1,460 mg/kg/day for water extract and 1,025 mg/kg/day for ethanol extract), 3,000 and 5,000 mg/kg. The satellite group was given the same dose of both extracts for 90 days and observed thereafter for 14 days in order to study the reversibility of the adverse effects. The results revealed that none of the Rang Chuet extracts altered the general behavior or mortality or changes in the gross morphology and any histology of the rats’ visceral organs. For sub-chronic toxicity, the result showed that the treatment of ethanol and water Rang Chuet extracts had no significant effect on average body weight, relative organ weights, histopathology of organs, clinical biochemistry, hematological parameters or liver enzymes. This analysis of by-products of a lipid peroxidation study suggested a trend of decreasing malondialdehyde levels in most of the Rang Chuet treated groups.

In conclusion, the safety value of Rang Chuet water extract and Rang Chuet ethanol extract in rats is 50 mg/kg body weight which indicate safe dose of Rang Chuet dried powder is 10.27 g/60 kg body weight per day.