It is well documented in Ayurvedic texts that metals are used in some Ayurvedic formulations. As in Modern Medicine they describe the adverse effects a medicine can cause to various body systems, similarly harmful effects of metallic medicines are also well documented. For example in "Purva Khand of Bhava Prakash Nighantu" (Dhatu-upadhatu Prakaran: verse 13) it is written, "Consumption of Impure gold 'bhasm' (ashes) or pure gold 'bhasm' consumed improperly may destroy strength, shukra dhatu (reproductive tissue), cause diseases and even death". The antidotes of toxicity or management of symptoms caused due to consumption of metallic medicines are also vastly described.
There is a section in Ayurveda called "Rasa shastra" which describes the use of metals, gems, minerals and poisons for manufacturing special formulations to combat chronic and difficult diseases. Rasa Shastra can be called "Vedic Chemistry". As the modern laboratory chemicals were not invented in the Vedic era (3000 years ago), herbal juices were used instead. Although the methods, of testing these metallic medicines described in Rasa Shastra, sound outdated or unscientific, they seem be based on some chemical principles. Because medicines declared non-toxic through these methods do not create any harmful effects in the body. Not only they are harmless, they work like 'steroids' used in modern medicine and can do miracles in difficult disease conditions or even the 'incurable' diseases.
They are not toxic metals but non-toxic herbo-metallic compounds
These Ayurvedic metallic medicines pass through extensive processing before they are declared fit for internal use. The metals, gems and minerals are first purified and then burnt several times and converted to 'bhasm' (ash). Each time before burning, the metallic powders are processed with fresh herb juices to neutralize their toxicity. Some of the metals are burnt up to one hundred times to make sure the heaviness or toxic effect of the metal is nullified. Once the 'bhasm' is ready it is tested for toxicity. One of the numerous tests the "bhasm" has to pass through is called 'varitar' which means the 'bhasm', once ready for internal use, floats on water indicating non-existence of heavy metal in it. The 'bhasms' are then transformed to compound formulas by mixing herbal powders. Special herbal juices are used for processing the compound formula. Thus these are no more toxic metals but non-toxic herbo-metallic compounds. The modern chemical testing might still indicate the presence of that metal in these compounds but according to Ayurveda, these metals have been transformed to non- toxic form, which is safe for internal use.
These lighter forms of metals (bhasm) contained in herbo-metallic
compounds work as carriers (yogavahi). This means they are able to carry
the herbs (mixed with them) faster to the desired site and start the
action immediately. They increase the bioavailability of the herbs to
the cell. They act as catalysts. After performing the desired action
these harmless light metals (bhasm) are eliminated out of body through
our waste excretory systems (urine and stool).