The word Rasayana is formed by two words 'Rasa' + 'Aayana' here 'Rasa' means 'Rasadi dhatus' i.e. the bodily tissues - and 'Aayana' means nourishment. Thus together it means that Rasayana is that which nourishes the bodily tissues.

The importance of Rasayana is that it is said to be none among the 8 parts of 'Aastanga Ayurveda'. It is also known by the fact that Charaka has mentioned about Rasayana in 'chikitsa stana' of 'charaka samhita' as one chapter.

Rasayana does not just mean that it nourishes the body. Along with nourishment it does have much more properties to it, which is as follows:

"Dheergamaayuhu smriti Medhamaroghyam tarunam vayah |
Prabhavarna swaroudhiarya dehendriya bala param ||
Vaksiddhi pranati Khanti labhate no rasayanat |
Labhopayo hi shasthanam rasadinam rasayanam ||"

It means by adopting rasayana therapy, the longetivity of life of a person increases, his memory improves grasping power increases, the person becomes young, energetic his complexion increases, his speech improves, his body and sense organs get strength etc. Thus 'Rasayana' on the whole is one, which improves the strength of body and mind and gives longevity of life. This "Rasayana" in a subtle form helps in treating the disease also that is why charaka has mentioned about in it 'chikitsa sthana'.

This Rasayana therapy is done in two ways:
(a) 'Kuti praveshika Rasayana'
(b) 'Vatatapika Rasayana'

A. 'Kuti Praveshika Rasayana'
In this type of Rasayana therapy, a 'kuti' or a hut is built in the wood of medicinal tree. This 'kuti' should be to the east, having a river near by. The surrounding area should be clean.

The person, who wants to undergo this therapy, should undergo 'shodhana therapy' first and then enter this 'kuti' after performing puja. He should stay in this 'kuti' for 3 months away from sun and wind and consume only the 'Rasayanas' like 'Brahma-rasayana' or 'chyavanprash' etc along with milk. This 'kuti'' will be equipped with all the necessary things required by the patient prior to his entry into the 'kuti'. Thus after staying 3 months in this 'kuti' when the person comes out, he is completely nourished and all the required qualities of 'Rasayana therapy' are got. This is 'kuti praveshika Rasayana'.

B. 'Vatatapika Rasayana' In this type of therapy 'Rasayanas' are taken while one is doing his daily chores staying in sun and wind, i.e. he it is not kept away in 'kuti' and 'Rasayanas' are consumed by him as a route without any restrictions.

Sushrutha has classified this 'vatatapika Rasayana' into three types:
(1) 'Kamya Rasayana'
(2) 'Naimittika Rasayana'
(3) 'Ajasrika or Nithya Rasayana'

(1) 'Kamya Rasayana': It is same as 'vatatapika Rasayana' mentioned above. Here 'Aswagandhadi lehya' or 'Ksheera paka' etc is taken for very long time which nourishes the 'sapta dhatus', 'Bala' etc.

(a) 'Naimittika Rasayana': - Here the Rasayanas taken acts both as a curative therapy for the disease as well as rejuvinative therapy. Eg: - 'vardhamana pippali Rasayana' in Rasayana or Rejuvination Therapy

To Be Continued...