Metals and minerals are an important aspect of Siddha medicine—an ancient system of indigenous medicine practiced in south India. Formulations containing a significant proportion of heavy metals such as mercury, arsenic, copper, etc., have been prescribed since centuries with no reports of toxicity. Several such formulations are successfully used in the management of diseases such as cancer and AIDS. Concerns have been raised over their presence in these medicines. Siddha practitioners claim that the mode of preparation of the drug renders them non-toxic. Metals are claimed to be completely transformed into inert compounds or ores through a multistep processing involving extremely high temperatures before being prescribed as medicines. Several papers have reported experimental proof of non-toxicity of several such formulations. However questions remain about the safety of these preparations till appropriate methods of analysis can actually reveal the difference in the elemental nature of these metals post absorption in the body. This may be much similar to the current knowledge of the differences in the absorption, bioavailability and ability to be retained in bone tissue of different forms of calcium. The high heat and presence of other plant-based preparations (that could chelate) in the extract could be altering the very nature of the metals post processing. Innovative methods of elemental analysis of these preparations along with that of the raw material shall be supportive evidence that can substantiate the claims of safety of these drugs in animal experimentation