Rasāyana, रसायन is a Sanskrit word, with the literal meaning: Path (āyana) of essence (rasa). It is a term that in early ayurvedic medicine means the science of lengthening lifespan, and in later (post 8th-century) works sometimes refers to Indian alchemy.
The name of the science of Indian alchemy or proto-chemistry, is more generally "The Science of Mercury", or Rasaśāstra, रसशास्त्र in Sanskrit, Nepali, Marathi, Hindi, Kannada and several other languages. Early Indian alchemical texts discuss the use of prepared forms of mercury or cinnabar (see samskaras). However, there is also ample mention of the preparation of medical tinctures in the early science of Indian alchemy.
Significant progress in alchemy was made in ancient India. An 11th-century Persian chemist and physician named Abū Rayhān Bīrūnī reported that "They have a science similar to alchemy which is quite peculiar to them. They call it Rasâyana, a word composed with rasa, i.e., gold. It means an art which is restricted to certain operations, drugs, and compound medicines, most of which are taken from plants. Its principles restore the health of those who were ill beyond hope, and give back youth to fading old age..." Raseśvara, a school of Indian philosophy was focused on finding Moksha: perfection, immortality, liberation using mercury. As such it focuses its efforts on transumation of the human body: from mortal to immortal. Many are the traditional stories of alchemists still alive since time immemorial due to the effects of their experiments. The texts of Ayurvedic Medicine and Science have aspects similar to alchemy: concepts of cures for all known diseases, and treatments that focus on anointing the body with oils.
Since alchemy eventually became engrained in the vast field of Indian erudition, influences from other metaphysical and philosophical doctrines such as Samkhya, Yoga, Vaisheshika and Ayurveda were inevitable. Nonetheless, most of the Rasayāna texts track their origins back to Kaula tantric schools associated to the teachings of the personality of Matsyendranatha and the lineage of the Natha Siddhas.
Two famous examples were Nagarjunacharya and Nityanadhiya. Nagarjunacharya was a Buddhist monk who, in ancient times, ran the great university of Nagarjuna Sagara. His famous book, Rasaratanakaram, is a famous example of early Indian medicine. In traditional Indian medicinal terminology "rusa" translates as "mercury" and Nagarjunacharya was said to have developed a method to convert the mercury into gold.
Rasayana therapy enriches rasa with nutrients to help one attain longevity, memory, intelligence, health, youthfulness, excellence of luster, complexion and voice, optimum development of physique and sense organs, mastery over phonetics, respectability and brilliance.
In pursuit of these matters, herbal prescriptions with many herbal substances, preserved in ghee and honey are given. Chyawanprasha is one of the traditional rasayanas. Specific adaptogenic herbs are also included in rasayanas including haritaki, amla, shilajit, ashwaganda, holy basil, guduchi and shatavari.
The whole, aqueous, standardized extracts of selected plants (Tinospora cordifolia, Asparagus racemosus, Emblica officinalis, Withmania somnifera, Piper longum and Terminalia chebula) were administered orally to experimental animals, in a dose extrapolated from the human dose, following which they were exposed to a variety of biological, physical and chemical stressors. These plants were found to offer protection against these stressors, as judged by using markers of stress responses and objective parameters for stress manifestations. Using a model of cisplatin induced alterations in gastrointestinal motility, the ability of these plants to exert a normalizing effect, irrespective of direction of pathological change was tested.... All the plant drugs were found to be safe in both acute and subacute toxicity studies. Studies on the mechanisms of action of the plants revealed that they all produced immunostimulation. The protection offered by Tinospora cordifolia against stress induced gastric mucosal damage was lost if macrophage activity was blocked. Emblica officinalis strengthened the defence mechanisms against free radical damage induced during stress. The effect of Emblica officinalis appeared to depend on the ability of target tissues to synthesize prostaglandins. Recent data obtained with Tinospora cordifolia have led researchers to suggest that it may induce genotypic adaptation, further opening the arena for more research and experimentation.
Puri has given detailed account of Classical formulations such as Amrit Rasayana, Brahm Rasayana, Jawahar Mohra, Kamdugdha Ras, Laxami Vilas Ras, Laxman Vilas Ras, Madanoday Modak, Makrdhawaj vati, Manmath Ras, Mukta Panchamrit Rasayana, Nari Kalyan Pak, Navjeevan Ras, Navratna Ras, Navratnakalp Amrit, Panchamrit Ras, Paradi Ras, Ramchuramni Ras, Rattivalbh Pak, Shukar Amrit Vati, Smritisagar Ras, Suvarn Malini Vasant, Suvarn Vasant Malti, Swapanmehtank, Vasant Kusmakar Ras, Visha Rasaayana, Vrihda Vangeshwar Rasa.
These classical Rasayan formulas, contain a large number of ingredients, including minerals, pearl, coral and gems, and include a specially processed (samskara) mercury (the word ras indicates mercury as an ingredient). Because of negative publicity and cost factor, the use of the classical rasayana formulas has declined considerably, and most of the preparations available now have herbal ingredients with a couple of mineral and animal products. The non-availability and wild life protection act has made the use of musk, amber, and parts of wild-life animals nearly impossible.
The current Rasayan formulas are based on such ingredients as amla (Emblica officinalis) which, if fresh, has high content of vitamin C, Terminalia belerica, Terminalia chebula, Shilajit, Long pepper, Black pepper, Ginger, processed Guggul, Guduchi, Ashwaganda, Shatavari and similar ingredients.
Rasayan Shastr in Ancient India was much less developed than today. Nevertheless, the use and practice of Rasayan was widespread in Ancient India, and some examples of applied rasayan include paints used in the caves of Ajanta and Ellora, Maharashtra state, the steel of Vishnustambha (literal meaning: the tower of Vishnu), and a processed wood sample in the Kondivade caves near the Rajmachi fort in Maharashtra.
In many Indian homes, rasayana (fruit squash) juices are prepared and served as drink, desert or as accompaniment to meals. In Tulunadu region of India, Banana and Mango Rasayana are made by mixing fruit pulp with cow's milk or coconut milk to a thick consistency. This rasayana may be drunk as juice by diluting with water or milk. With thick consistency it is used as accompaniment to Dosa, Chapati or meals. Rasayana may also be known as lassi. Many believe this rasayana helps to beat the heat of Indian summers.