Ayurvedic Concepts for Medicines Adverse Reactions
There is a popular misconception that ayurvedic medicines are devoid of adverse reactions. However, the Charaka Samhita , which is a classic text book of ayurveda, describes all the adverse reactions to medicines when they are prepared or used inappropriately. Attention is given to factors like the physical appearance of the part of the plant to be used ( prakriti ), its properties ( guna ), actions ( karma; prabhava ), habitat ( desh ), season in which it grows ( ritu ), harvesting conditions ( grahitam ), method of storage ( nihitam ) and pharmaceutical processing ( upaskritam ), which must be considered while selecting the starting material that goes to form the medicine. Similarly, Charaka also describes, elegantly, several host-related factors to be considered when selecting medicines in order to minimize adverse reactions like the constitution of the patient ( prakriti ), age ( vayam ), disease ( vikruti ), tolerance (previous exposure) ( satmya ), psychological state ( satwa ), digestive capacity ( ahara-shakti ), capacity for exercise ( vyayama shakti ), quality of tissues ( Sara ), physical proportions of the body ( sahanan ) and strength ( bala ).
Interestingly, classical ayurveda prescribes metals and minerals as medicines given as bhasmas (incinerated mineral formulations) or in combination with plants as herbo-mineral formulations (e.g., Arogyavardhini ). Manufacturing procedures for these medicines are stringent, and adverse reactions are described when precautions are not taken while manufacturing and administering these medicines. Although these medicines are widely used in India, doubts about their long-term safety come up due to the presence of toxic metals in them  and there are reports related to adverse reactions.
To summarize, Charaka says, "that even a strong poison can become an excellent medicine if administered properly. On the other hand even the most useful drug can act like a poison if handled carelessly".