This review aims to explore the toxicological aspects of mercury-based herbo-metallic preparations like cinnabar and "Rasasindura" that are primarily composed of mercuric sulfide (HgS). Cinnabar-containing preparations have been used extensively in Indian and Chinese systems of medicine for treatment of chronic ailments like syphilis, high fever, pneumonia, insomnia, nervous disorders, deafness, and paralysis of the tongue. Contrary to Western medicine, which does not promote the use of mercury due to its toxic effects, Indian and Chinese traditional practitioners believe that mercury-based formulations have potent therapeutic efficacy, while there is no toxicity due to the unique and repeated purification processes employed during preparation. However, lack of proper pharmacovigilance and widespread self-medication has resulted in undesirable effects to certain sections of the consumers of these preparations, which have contributed to the negative publicity for these forms of medicine. Variations in the quality of the preparations coupled with the lack of understanding of the differences in the recommended dosages and treatment strategies adopted by traditional medicine practitioners, further fuels concerns in the Western world on the safety and efficacy of traditional medicine. But in spite of these concerns, concerted efforts to understand the biological interactions and transformations of these preparations are yet to gain momentum. Although scattered reports on the toxicity of these preparations are available in literature, their mechanism of action has not been conclusively established. Long-term pharmacotherapeutic and in-depth toxicity studies are needed to address the apprehensions raised by these herbo-metallic preparations. This review highlights the lacunae in the studies conducted thus far, and assesses the need for further studies to provide significant data to establish the safety and efficacy of such preparations, as well as develop gold standards for stringent quality control of these preparations.

Sulphur has been used through ages as a panacea in the Ayurvedic system of medicine 1. It has been used extensively in the preparation of drugs like Rasasindura 2 , Panchamrita parpati 3 , Kajjali 4 , Shila Sindoor 5 , Swarna Makshika 6 and many other Ayurvedic formulations. Mainly it is used to process mercury. It is believed that the toxic effects of mercury are avoided by combining with sulphur 4. The mercury and sulphur are subjected to mechanical grinding in a mortar to obtain a black powder of β-HgS. This black powder is subjected to a controlled heating process to obtain Rasasindura (α-HgS). It is well known that sulphur forms covalent linkages to mercury 7. This leads to formation of mercury sulphide, which is insoluble in the gastrointestinal tract and hence non-toxic 6. According to Ayurveda, sulphur has to be purified before being used in combination with other formulations 8. The purification process is carried out using butter/ghee and milk, resulting in certain chemical transformations and removal of impurities from raw sulphur. Thus far, there is no scientific evidence to prove this. This study was carried out to assess and scientifically validate the role of the purifying agents in the chemical transformation of sulphur.

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