Cause of illness in Human Being is due to Disturbances in Metabolism. Metabolism depends on Hormones-Enzymes secreted from vital organs like liver, Pancreas, Pituitary Gland etc...
Modern life style-stress, Food Habits, Polluted Food, Water and Environment Affects our body and vital organs. Hence Illness occurs. Mother Nature has created some Divine-Hollistic plants which has Life-Force Energy Resembling to human body.
The great thing about Ayurveda is that its treatments always yield side benefits, not side effects.