Vipaka comes under the five concepts under the study of a dravya (Rasapanchakas). In Ayurveda the digestion & metabolism of any substance is explained in two stages: Avasthapaka Nishtapaka Avasthapaka is the first phase considered as digestion. In charaka the word “prapaka” is used as the synonym for avasthapaka. Nishtapka or Vipaka is the second phase and considered as metabolism.