Vipaka is one of the 5 qualities of a dravya (substance). Vipaka is the end effect of metabolism. It is related to the rasa of a dravya but manifested only after the dravya comes in contact with the agni i.e. digestive fire in the body. Thus vipaka is that quality of a substance which is associated with rasa of a substance as well as the stage of metabolism or transformation of a dravya after its consumption. It holds specific significance in the field of Ayurvedic pharmacology and dietetics. The action of a dravya inside the body after its metabolism can be understood to some extent if the vipaka of a dravya is known. Every dravya or substance has its own rasa(taste) and when this rasa encounters jatharagni or digestive fire it transforms into vipaka. Rasa undergoes metabolic changes and vipaka is the metabolic end effect of a dravya(substance).
The term 'Vipaka' is composed of 2 parts. वि + पच 
- Vi : it stanads for Vishista
- Pa : paka means pachanam or digestion
Thus, The term vipaka indicates the specific transformation of a dravya after its metabolism inside the body. This specific quality generated after transformation is called as 'Vipaka' in Ayurveda. It is defined by Acharya Vagbhata as,
जाठरेणाग्निना योगाद्यदुदेति रसान्तरम् | रसानां परिणामान्ते स विपाक इति स्मृतः ॥ (Asht. Hrud. 9.20)
jāṭhareṇāgninā yogādyadudeti rasāntaram | rasānāṁ pariṇāmānte sa vipāka iti smr̥taḥ ॥ (Asht. Hrud. 9.20)
Meaning: The digestive fire or jatharagni when comes in contact with rasa of a certain dravya or ahara(food) it transforms into vipaka at the end. Thus the end effect of the rasa(taste) can be termed as vipaka.
The concept of Avasthapaka and Nishthapaka
Avasthapaka and nishthapaka are 2 distinct concepts in Ayurveda. Nishthapaka means vipaka while avasthapaka is the quality displayed during the transient state of food during the process of digestion. Vipaka is constant quality of a substance post digestion or transformation while, avasthapaka is temporary stage. Both of them have effect on body components and health. Avasthpaka is constant for any dravya whereas nishthapaka or vipaka is specific to the dravya and related to its rasa.
According to Ayurveda at a very basic level, Ahara or food is digested in two main stages, awasthapaak(initial stage) and nishthapaak or vipaka(end stage)
Awasthapaka (initial stage)
अन्नस्य भुक्तमात्रस्य षड्रसस्य प्रपाकतः|
मधुराद्यात् कफो भावात् फेनभूत उदीर्यते|
परं तु पच्यमानस्य विदग्धस्याम्लभावतः|
पक्वाशयं तु प्राप्तस्य शोष्यमाणस्य वह्निना|
परिपिण्डितपक्वस्य वायुः स्यात् कटुभावतः| (char. chik.15)
When the food is ingested, it undergoes various metabolic changes in our digestive tract, it does not remain in that same state. thus, the process in which the food changes, its state is known as awasthapaak. This occurs in three stages.
1) Prathama awasthapaka(first level of initial stage of digestion) wherein the food gets digested and changes its form in aamashaya or stomach with the help if madura(sweet) Rasa. Here kapha is produces which is like froth.
2) Dwitiya awasthapaak(second level of initial stage of digestion) wherein the semi digested food leaves the stomach and changes its form further with the help of amla(sour) rasa. Here pitta is produced.
3) Trutiya awasthpaak(third level of initial stage of digestion) wherein the food changes its form into solid mass in intestine with the help of katu rasa. Vata is produced in this process.
Nishthapaka or Vipaka (End stage)
Nishthapaka is the term synonymously used with the term vipaka. Vipaka of a dravya is specific to its rasa. Ayurveda treatises clearly explain which rasa generates which vipaka. In general, it is described that,
परं चातो विपाकानां लक्षणं सम्प्रवक्ष्यते ॥
कटुतिक्तकषायाणां विपाकः प्रायशः कटुः | अम्लोऽम्लं पच्यते स्वादुर्मधुरं लवणस्तथा ॥ (Char. Samh. 26.57-58)
paraṁ cāto vipākānāṁ lakṣaṇaṁ sampravakṣyate ॥
kaṭutiktakaṣāyāṇāṁ vipākaḥ prāyaśaḥ kaṭuḥ | amlo'mlaṁ pacyate svādurmadhuraṁ lavaṇastathā ॥ (Char. Samh. 26.57-58)
Meaning: It is the finally transformed state of food or dravya (substance) after digestion. After the initial digestion phase, the food is assimilated for the further nourishment of dhatus in this process. The metabolism of any dravya in this context is based on rasa(taste) since it can be perceived, but their end effect can only be inferred by their actions in our body. On this basis vipaka can be understood as follows.
Substances having katu, tikta, Kashaya rasa are transformed into katu vipaka.
Substances having amla rasa are transformed into amla vipaka and those having madhura and lavana rasa are transformed into madhura vipaka.
But there exists a set of certain drugs which have an unexpected end effect or vipaka in our body according to some ayurvedic scholars.
Types of Vipaka
According to ayurvedic acharyas(scholars) there is difference of opinion and theories when it comes to the classification of vipaka. But at the tip of iceberg the types are as follows.
1. Shadvidha vipaka vada(concept of 6 vipaka) [sush.sutr.40.10]
2. Panchavidha vipaka vada(concept of 5 vipaka)[sush.sutr.26.524]
3. Trividha vipaka vada(concept of 3 vipaka)[char.sutr.26.63],[ash.su.1.17]
4. Dvividha vipaka vada(concept of 2 vipaka)[sush.sutr.40.10]
So, to summarize the basic types of vipaka and its effect on dosha;
VIPAKA GUNA(PROPERTY) DOSHA
Madhura Snigdha,guru Increases kapha
Amla Snigdha,laghu Increases pitta
Katu Ruksha,laghu Increases vata
Importance of Vipaka
(According to sush.sutr.40.10)
The concept of vipaka is important to Ayurveda because the guna and dosha of dravya is dependent on the end effect of metabolism that is vipaka. Which means if a certain drug is digested with the help of proper jatharagni(digestive fire) then the guna(property) of that drug is enhanced, whereas if there is no proper digestion of that drug then dosha imbalance can be seen.
- Shabdakalpadruma See Vipaka
- Ashtanga Hrudayam (Sutrasthanam Adhyaya 9 Sutra 20)
- Chakrapani commentary on Charaka Samhita (Chikitsasthanam Adhyaya 15 Sutram 9-11)
- Charaka Samhita (Sutrasthanam Adhyaya 26 Sutram 57-58)