[Mridu(mild)] The drugs with low quality, less effective, mixed with antagonistic drugs, used in lesser doses, in person having excessive dryness in the body (without snehana & swedana) acts slowly and are called as mridu.
अकृत्स्नदोषहरणादशुद्धी ते बलीयसाम्| मध्यावरबलानां तु प्रयोज्ये सिद्धिमिच्छता||५७||
The madhya & mridu categories of drugs and their effects are not enough to expel the complete morbid doshas from the body, hence are suitable only for madhya & avara bala person for shodhana.
The diseases are classified as severe, medium & mild when it has all, medium, & few signs and symptoms respectively. The three categories of drugs are planned and administered respectively in three groups of diseases with due consideration of bala (strength) of person & disease.