One has to understand the nature of koshtha (whether guru or laghu) and the strength of the body for giving either mild (mridu) or potent (teekshna) medicine.
वमनं न तु दुश्छर्दं दुष्कोष्ठं न विरेचनम्| पाययेतौषधं भूयो हन्यात् पीतं पुनर्हि तौ||३७||
Never give emetic drug to people who are unsuitable for vamana; virechana to those with unsuitable koshtha, if medicine intake happens in such conditions it may even lead to death.
Ayoga happens when asnigdha (under-oleated) and asvinna (under-sudated) person with ruksha nature of the body, is administered a recipe, which is stored for long duration. Here, the drug is unable to remove doshas from the body by creating dosha-utklesha.
Such a condition will lead to symptoms like vibhramsha (virechana oushadha will lead to vamana and vice versa), swelling, hiccups, black-out, cramps in calf muscle, itching, fainting and discoloration.
स्निग्धस्विन्नस्य चात्यल्पं दीप्ताग्नेर्जीर्णमौषधम्| शीतैर्वा स्तब्धमामे वा दोषानुत्क्लिश्य नाहरेत्||४०||
Ayoga happens in the following conditions too : • Even after proper sneha-sweda there is sub-optimal dose of medicine • Due to increased agni (digestive capacity), quick digestion of medicine happens If there is ama dosha, the medicine for vamana will not work in the desired manner. The case is similar also with virechana drugs.