Dr.Urmila Thatte
The origins of Ayurveda, the traditional Indian System of Medicine can be traced back over 6000 years. Having divine origins, this science of life relies heavily on drugs for therapy although there are non-pharmacological treatments also described. In fact, Jeevaka, an ancient physician is credited to have said that there is no plant on the face of the earth that will not have some medicinal property. As we stand at the threshold of the 3rd Millenium, it is imperative to look back, introspect and enquire whether there are any unpolished gems lying unexplored in the vast treasures of Ayurvedic medicine, especially with respect to drugs. Pharmacology, which is the speciality dealing with drugs, is very rich and elaborate in Ayurveda. It is described under the subject “dravyagunavigyan” and has in its repertoire different medicinal plants to be used either alone or in combination. Several minerals as well as animal products are also elaborated in the compendia. The medicines described in Ayurveda can give leads for the development of new drugs. This has been amply illustrated by the success met with the development of reserpine from Rauwolfia serpentina (sarpagandha), guggul from Commiphora mukul or an immunostimulant from Tinospora cordifolia. However, more interesting and exciting is the underlying philosophy in explaining the actions of the drug. It is evident that Ayurveda is an experimental science and most of the teachings of the subject are based on extraordinarily astute observations. Thus, for example, actions of a drug have been explained on the basis of several features such as its rasa, veerya, vipaka, prabhava and guna. Thus, although pharmacokinetics in Ayurveda appears antiquated because no measurements of drug levels were performed, the concepts of how the body must be handling drugs become evident when one examines these concepts. This article focuses on these general principles of drug action as described in Ayurveda and discusses some possible approaches to validate these in the light of current science.
Over the years, the pharmacopoeia of Ayurveda grew and matured through grass-root contact with the populace who used it. Merging with and picking from rich local traditions, this science has an imposing repertoire of medicines.
As we stand at the threshold of the 21st century today, it is imperative to look back, introspect and inquire whether there are any unpolished gems lying unexplored in the vast treasures of Ayurvedic medicine, especially with respect to drugs. The whole canvas of Ayurvedic pharmacology is as vast as the horizon itself. It is impossible to cull this into a series of articles let alone one single article. This paper will therefore attempt to discuss only some of the fascinating aspects of Ayurvedic pharmacology, which are novel and different from the ideas of modern pharmacology.
Ayurvedic Pharmacology: Basic concepts
Pharmacology, which is the speciality dealing with drugs, is very rich and elaborate in Ayurveda. It is described under the subject “dravyagunavigyan” and has in its armamentarium different medicinal plants to be used either alone or in combination. Several minerals as well as animal products are also elaborated in the compendia. Ayurveda believes that medicines (and these could be drugs or dietary substances) are created from the specific combinations of the panchamahabhoota (or the 5 elements that form all matter on earth). These medicines are used to keep humans healthy (a philosophy much emphasized in Ayurveda) as well as treat disease when it occurs. Dravyagunavigyan deals with the properties, actions, uses, doses, time of administration as well as the formulation of drugs.
The study of materials (padarthavigyan) forms the basis of pharmacology in Ayurveda. Thus, Ayurveda has described drugs to have 7 specific features. These are used to characterize and predict the therapeutic action of a drug. These are:
Dravya / drug
Rasa taste
Guna property
Veerya potency
Vipaka metabolite
Prabhava specific properties
Karma action
Ayurveda was an observational science: entirely experimental. Thus, ancient Ayurvedic scholars first classified drugs according to the tastes they had. Specific tastes were to have specific effects. Thus, for example, sour substances would increase pitta or conversely, sweets would reduce pitta. Unfortunately, certain drugs defied this classification. Thus, lime which is a classically sour substance does not increase pitta but rather reduces it (lime-juice is used in hot summer months as a cooling substance). Hence, the Ayurvedic physicians came up with another concept of vipaka; i.e. they suggested that drugs would be converted in the gut into metabolites, which would have characteristics different from the parent substances. These would then explain the effects a drug produced. Thus, lime, having amla rasa was converted in the gut into a madhur vipaka. This had the property of reducing pitta, which explained its action. However, there were further problems. Sometimes, drugs with similar rasa and vipaka produced different actions. The concept of prabhava was born. Prabhava was the specific property of a drug, which classified it into that particular group e.g. Terminalia arjun had a cardiac prabhava or Embelia ribes was anti-helminthic because of its own peculiar property. This, unfortunately, was given as the ultimate solution: no further questions were asked at this stage and no answers provided for effects.
Let us examine each of these properties in some detail.
Guna
The guna of a drug is its property. These properties again help to predict the action of drugs. Charaka has described a total of 41 gunas to drugs. These were classified broadly into 3 groups:
Vaisheshik (5 in number) and related to the panchamaphabhoota and the five senses,
Samanya or general (30 in number) and
Atma (6 in number) and related to emotions.
The samanya guna were further divided into 20 gurvadi and 10 paradi gunas. Of these the 20 gurvadi gunas are used commonly and fall into the category of common gunas as they are easily found among substances on earth. These 20 are actually 10 pairs, each guna having the opposite activity of its pair. Of these 20, only 8 are more often referred to in day to day practice. These are again described according to their elemental composition, which influences their characteristic. The gunas include
Guru (heavy) laghu (light)
Sheeta (cold) ushna (hot)
Snigdha (lubricated, supple) rooksha (dry,rough)
Manda (slow) teekshna (sharp)
Thus, a substance that is guru (e.g. condensed milk, masha-udid dal) contains prithvi or earth (therefore increasing kapha dosha predominantly) as well as water or jal as the major components, and is difficult to digest. In the process of digestion, a guru substance can spend the agni and cause mandagni, a condition that leads to several disorders. These substances are nutritive, in that they cause growth. On the other hand, the laghu medicine is easy to digest, is light and contains akash (space), vayu (wind) and agni (fire). Because of these, laghu substances tend to increase vata dosha and reduce kapha dosha. They are useful in weight reduction and wound healing, as well as in disease where there is an excess of guru guna e.g. diabetes, fever, ulcerative colitis.
The “cold” and “hot” concepts of Ayurveda are very interesting. Drugs are believed to be either cold (sheeta) or hot (ushna) and these properties, in turn influence their effects. The sheeta substances reduce pain, thirst and giddiness, effects opposite to those produced by the ushna agents. Containing a predominance of jal (water), sheeta substances reduce pitta, but increase vata and kapha. They exert a diuretic effect, are stryptic, and improve tissue quality. Sandalwood and durva (a typical kind of grass) are sheeta in nature.
Ushna drugs (which contain agni as the predominant element) increase pitta dosha, cause sweating, pain, thirst, and giddiness and improve digestion by stimulating agni. Piper longum, dried ginger (Zinriber officinalis) or soontha, pepper and chilli exemplify ushna medicines.
The concept of snigdha indicates the process of lubrication. The skin becomes soft and supple and doshas are more easily expelled. Because of this, snigdha substances like ghee and oil are used before panchakarma therapies given for expulsion of abnormal doshas. The opposite guna is rooksha (dry). Substances with rooksha qualities contain vayu and therefore increase vata and decrease kapha and pitta. These agents strengthen tissues and dispel lethargy. Terminalia chebula and Plumbago zeylenica are examples of rooksha drugs.
The last two commonly encountered gunas are manda (slow) and teekshna (sharp). Manda drugs increase kapha and decrease pitta. As these agents contain earth and water, they are useful to increase tissue growth. Asparagus racemosus and Hemidesmos indica are examples of manda guna. The teekshna guna confers on agents like pepper, Plumbago zeylenica, seasame, and Balio montanum the ability to stimulate agni (and therefore digestion). However, just like ushna substances, these agents can cause pain, help in weight reduction and destroy tissues.
Rasa Concept
The word rasa has several connotations in Ayurveda. These include
Rasadhatu: This is the primordial tissue and gives an anatomical connotation to the word
Rasashastra: The science which deals with the therapeutic use of mercury is referred to as this
Rasa: This word alone indicates the fresh juice extracted from the specific part of a plant e.g. juice of lime and has a pharmaceutical connotation.
Rasa: It also indicates the taste of the substance.
We are concerned in the current discussion with the last meaning. Ayurveda has described that all medicinal substances (i.e.dravya) can be classified into 6 groups according the tastes they have. These tastes along with examples are given in Table 1.
The properties of the 6 Rasas (according to Charaka)
The characteristic properties of a medicine belonging to that particular group is because of the predominance of specific elements of the panchamahabhoota. The first basic principle is that all rasas are made up of variable amounts of all the 5 basic elements [namely, space (akash), wind (vayu), water (jal), earth (prithvi)and fire (tej or agni)]. The predominance of one or more elements confers on them the peculiar property or guna which in turn influences its action. As can be seen from Table 1, madhur rasa substances have a predominance of prithvi. This element therefore has a tendency toward increasing kapha dosha (which in turn has a predilection for fat tissue) and therefore madhur rasa substances tend to increase weight, and give strength to tissues. On the other hand, these drugs also help in reducing pitta or vata related diseases like gastritis and arthritis.
The rasa influences the ultimate action a drug produces and underlies its use in specific diseases. In kapha diseases, katu, tikta, and kashaya drugs are useful as they reduce kapha. First, katu rasa (pungent) is given to reduce the heaviness of the kapha followed by tikta (bitter) to reduce the “sweetness” and absorb the thinned out kapha. Finally, the kashaya rasa (astringent) will help in throwing out remnants of the kapha as well as restore balance.
In pitta diseases, tikta (bitter) rasa helps in digesting undigested food particles (called as ama and believed to underlie many diseases) and increase agni. This is followed by drugs which are madhur rasa having “cold” in nature. These further reduce pitta. Kashaya drugs then expel the vitiated pitta.
In vata diseases, lavana drugs are given first to reduce vata followed by amla medicines to remove obstruction to channels. Lastly, madhur rasa drugs are given to further quieten vata.
An important feature of rasa is that it is not a static feature: it is dynamic and can change under specific environmental and other influences. Thus, lapse of time, the vessel in which it is stored, the process of cooking, combination with other substances, ripening, drying in the sun, place of harvest, and bacterial modification (souring or spoiling) are some of the factors which can modify rasa.
The six Rasas can be divided into 2 groups according to whether they contain the element agni (fire). Thus, amla, lavana and katu contain agni and therefore increase pitta, cause giddiness and pain, while madhur, tikta and kashaya are milder, and do not contain agni, thus reduce pitta.
The rasa are identified not only by their physical characteristics like taste or by their actions onthe doshas, but also by the emotional responses they produce. Thus, madhur rasa (rice) produces satiation and a pleasurable feeling and amla (tamarind) cause intense salivation, sweating and itchy teeth.
As the study of drugs continued, it was observed that there were several plants which exerted effects which could not be explained on the rasa alone. Hence the further concepts of vipaka and prabhava came up to explain the karma of drugs.
Vipaka
After a drug is ingested, it is acted upon by the gut fluids containing enzymes, to give rise to a “final product” which is not visible to the naked eye. This is called the vipaka. Thus, the vipaka is defined as the product of the rasa, which occurs after the action of the jatharagni. The vipaka is absorbed, and through the rasa-dhatu (plasma) influences the entire body. The vipaka in turn is further digested for tissue consumption by the tissue agni (dhatvagni). The proper digestion of drugs to give rise to the correct vipaka is necessary for the appropriate action of the drug.
Charaka has described that the 6 rasa get converted to 3 vipaka. These are madhur, amla and katu. Madhur vipaka is formed from madhur and lavana rasa, amla from amla rasa and katu from the remaining three. The quality of the vipaka formed differs according to the rasa. Thus, the madhur vipaka formed of madhur rasa is stronger than that formed from lavana. The katu vipaka formed from katu rasa is the best, followed by that formed from kashaya and the last is that formed from tikta.
Veerya
Veerya is the property which gives the drug the power or potency to produce it action. This veerya is lost after a specific time period (an important point which is kept in mind when deciding the shelf-life of a drug). There are mainly 2 types of veerya, namely, sheeta and ushna (although the gunas, some physicians believe that there are 8 types). The action of a drug will be influenced by the veerya if this is more powerful than the rasa. For example, onion is katu rasa (i.e. pungent) and as such is expected to increase pitta. The actual observation is that onions are useful cooling agents. This is because they have sheeta-veerya. The same observation holds true for Piper longum (pimpli). Sugar cane juice has a madhur rasa and as such is expected to reduce vata, but because of its sheeta-veerya it actually increases vata. Emblica officinalis reduces pitta and is used in dyspepsia in spite of having a sour (amla rasa) because again of its sheeta-veerya.
Prabhava
Both Plumbago zeylenica and Balio montanum have katu rasa, ushna veerya and katu vipak. They both produce pro-kinetic effects but Plumbago zeylenica never causes diarrhea while Balio montanum can do so. This is the prabhava: or the specific property (characteristic) of the drug. The anti-pyretic effects of aconite and pearl are also because of their prabhava. Milk and ghee are both madhur rasa and sheeta veerya, but ghee is a good digestive (deepan) while milk is not. This feature of ghee is explained as its prabhava. Similarly, 2 kashaya rasa drugs like Terminalia chebula and Woodfordia fructosa produce opposite effects on the gut, the first increases motility while the second causes constipation (which is typical of the kashaya rasa). Thus, when rasa, guna, veerya and vipaka could not explain the effects of a drug, it was attributed to its prabhava.
General Pharmacological Principles
In general, the relationship between the rasa-veerya-vipaka is a given in Table 3. Exceptions exist to this rule. For example, pimpli (Piper longum) has a katu rasa and should have katu vipaka. Instead, it has a madhur vipaka and therefore exerts an anabolic effect. Further, the relative predominance in a medicine of its property (i.e. rasa-veerya-vipaka) also determines which is expressed. Red calotropis has ushna veerya and katu vipaka and should therefore be contraindicated in pitta related disease. However, because of its dominant madhur rasa, it is very useful in raktapitta. Similarly, dried ginger, which has ushna veerya and katu rasa, should be catabolic. Its anabolic effects are actually expressed because of the dominant madhur rasa.
The dominant veerya (ushna veerya) expressed in asafetida, which has katu rasa and vipaka and by rules ought to increase vata, actually reduces vata because of the veerya.
However, it is the combined action of all these properties which lead to the multi-faceted effects of plants. This is well illustrated in amrita or Tinospora cordifolia. The tikta rasa of this plant reduces kapha and pitta, the ushna veerya reduces vata (making the drug tridoshashamak), its madhur vipaka exerts anabolic effects and its prabhava is vataraktanashak.
Conclusion
We have seen that observation and logic forms the infrastructure on which the edifice of Ayurveda rests. Astute inferences have been drawn and explanations given for observed effects. The rasa-veerya-vipaka-prabhava concept forms just the tip of the iceberg which is Ayurvedic pharmacology. A science which encompasses many branches like pharmaceutics, pharmacognosy, pharmacodynamics etc. as well as teaches the philosophy of rational drug use requires detailed study. At the threshold of the 3rd millennium, Ayurvedic pharmacology offers a mine of information which needs to be tapped to enrich modern medicine.
Further Reading
Dahanukar SA & Thatte UM (1989) Ayurveda Revisited, Popular Prakashan, Mumbai
Dahanukar SA & Thatte UM (1996) Ayurveda Unravelled, National Book Trust, New Delhi.
Gogatay VM (1982) Dravygunavigyan, Continental Publications, Pune.
Dr Urmila Thatte is Professor and Head at the Department of Clinical Pharmacology, Seth GS Medical College & KEM Hospital, Mumbai. She has an M.D. and PhD in Pharmacology from the University of Mumbai, she is a Diplomate of the National Board of Examinations, New Delhi, in Clinical Pharmacology and a Fellow of National Academy of Medical Sciences, New Delhi. Dr Thatte serves on the National Pharmacovigilance Advisory Committee and is the Coordinator of the Regional Pharmacovigilance Centre of the National Pharmacovigilance Programme. She is on the WHO Expert Advisory Panel on Drug Evaluation, and she also serves on various Scientific Review committees as a Clinical Pharmacology expert of the Indian Council of Medical Research. Dr Tatte has over 120 Publications in National and International Journals including 8 books to her credit and was the Clinical Pharmacology Section Editor for Clinical Pharmacology for the API (Association of Physicians of India) Textbook of Medicine published in 2008. She has been the Course Director for Research Ethics in the Joint NIH-ICMR Training Program on Bioethics and has served as faculty on several national programs.
Dr Tatte is the Secretary of the Forum for Ethics Review Committees in India.
