The fundamentals of Ayurvedic drug action are scientific and based on the theory of Rasa, Guna, Virya, Vipaka and Prabhava which were the simplest parameters in those days to ascertain the action of the drug. Action of drug means to dismantle the Samprapti Ghatakas of the disease. Hence to explain the mode of action of a drug means to establish a relationship between the Samprapti Ghatakas of the disease and pentafold principles of Rasa, Guna, Virya, Vipaka and Prabhava of the drug.

The word Guna is derived from the root ‘ Guna Amantrane’ which means to invite or to attract. The word Guna has different meanings and interpretations in different fields of science. Guna according to Ayurveda , aims to provide information to understand the concept of Dhatusamyata. The term Guna finds place not only in understanding body but also to understand and evaluate drug action. This is the applied aspect of the quality known by the name Guna.

Charaka in the pattern and lines of Darsanasastras, listed 41 Gunas. Out of these Gunas 20 Gurvadi are of importance due to their scope for application in the clinical field.

In case of Cikitsa, Charakacarya advised to use the drugs having opposite Gunas for the treatment of curable diseases. Acaraya Susruta mentioned that the Gunas present in the drugs and the body are one and the same, hence the drugs having these Gunas are responsible for the normalcy of the body constituents.This description is evident that Guna is having the central role in understanding the physiology, pathology and the therapeutic applications of the drugs.

The word Guna is derived from the root "Guna Amantrane", capable enough to highlight the ability to attract or to invite. The word Guna has a number of meanings such as quality, property, secondary strands of rope, bow string, thread, deliberation merit, sense organ etc. The different meanings of the word Guna has related to different sciences / subjects. In the context of Ayurveda Guna is highlighted to denote Ayu (Cha. Su. 30) has been taken up.

GUNA NIRUKTI :
The etymology of the word indicates the feature of both Dravya and Guna, which refers to quality of attraction or invitation.
In clinical practice Ausadhi considered either "Dravyapradhan" or "Gunapradhan" or both, are to be used. In both the categories Gunasampat (Cha. Su. 16) is of utmost importance to achieve the object-

GUNA VYAKHAYA :
Ayurveda advocates six padarthas .Of these Guna is considered as main. Since Samanya and Visesh are usually explained in terms of Gunas (Cha. Sa. 6/9) Dravyas are classified based on functions related to Gunas (Cha. Vi. 8/10, Cha. Su. 26/46) Karmas are manifested forms of Gunas (Cha. Su. 26/71). Samavaya which is the eternal and intimate relation between Dravya and Guna (Cha. Su. 1/50). This also points to the importance of the concept of Guna.

NATURE OF GUNA :
Guna is one among the Sat Karan Padarthas according to Ayurveda. The concept of Guna occupies a preminent place in the principles of understanding the clinical conditions and therapeutics. Many scattered references regarding the "Guna Svarupa" are mentioned in Ayurveda.

According to the aims and objects, there are differences of opinion in "Guna Samkhya". Nagarjuna is the authority who believes that Gunas are infinite in numbers. (Visvalaksana Guna Rass.Vai.1/168). Cakrapani though the follower of the same concept (Asankheyatvat Gunanam: Cha. Chi. 24 Cakra.) classified 41 guna described by Charaka.

Among these Gunas twenty Gurvadi Gunas are of utmost importance because of their utility in the applied clinical science (Ca. Sa. 6/10) for the knowledge of Triskandha Ayurveda i.e. Hetu, Linga and Ausadha Skandhas.

1. Guru
2. Laghu
3. Manda
4. Teeskhsna
5. Ushna
6. sheetha
7. Ruksha
8. Snigdha
9. slaksha
10. Khara
11. Drava
12. Sandra
13. Kathina
14. Mrudu
15. Cala
16. Sthira
17. Slashana
18. Sthula
19. Vishada
20. Picchila

The inheritance qualities of Pancamahabhutas beyond which nothing is required to think upon for the physician are explained interms of Gurvadi Gunas (Pancamahabhuta Gunas - Ca.Su. 26) The Paradi Gunas belong to the physician or the researcher, are helpful to manipulate the effectiveness of the Gurvadi Gunas. It is clear from the above description that the Gurvadi Gunas are the most important among the Gunas, which are explained as the Saviparyaya Guna.