Mantra of the Medicine Buddha
Sanskrit Pronunciation
Tad-ya-ta: Om Bhai-sha-jye Bhai-sha-jye Maha Bhai-sha-jye Ra-ja Sa-mud-ga-te Sva-ha 
Tibetan Pronunciation
Tad-ya-ta: Om Be-kan-dze Be-kan-dze Ma-ha Be-kan-dze
Ra-dza Sa-mung-ga-te So-ha!

The mantra means:

May the many sentient beings who are sick,quickly be freed from sickness, And may all the sicknesses of beings Never arise again.
Ancient teachings tell us that merely seeing the Medicine Buddha, or even seeing an image of the Medicine Buddha, or hearing the name of the Medicine Buddha, can confer inconceivable benefits.
In Tibetan images of the Medicine Buddha the left hand typically holds a blooming myrobalan plant. Tibetan medicine recognizes three basic types of illness, the root causes of which are the conflicting emotions -- passion, aggression, and ignorance. Myrobalan is the only herb in the Tibetan pharmacopoeia that can aid in healing each of these three types of diseases. This is like the action of the Buddha of Healing, who has the power to see the true cause of any affliction, whether spiritual, physical or psychological, and who does whatever is necessary to alleviate it.
In his Teachings on the Medicine Buddha the Ven. Thrangu Rinpoche discusses the position of the Medicine Buddha's two hands:
"His right hand is extended, palm outward, over his right knee in the gesture called supreme generosity. In it he holds the arura, or myrobalan, fruit. This plant represents all the best medicines. The position of his right hand and the arura which he holds represent the eradication of suffering, especially the suffering of sickness, using the means of relative truth. Sickness can be alleviated by adjusting the functioning of interdependent causes and conditions by the use of relative means within the realm of relative truth, such as medical treatment and so on. The giving of these methods is represented by the gesture of the Medicine Buddha's right hand.
"His left hand rests in his lap, palm upward, in the gesture of meditative stability or meditation, which represents the eradication of sickness and suffering— and, indeed, the very roots of samsara— through the realization of absolute truth. From the point of view of either relative truth or absolute truth, the fundamental cause of sickness and suffering is a lack of contentment and the addictive quality of samsara. Therefore, to indicate the need for contentment, in his left hand he holds a begging bowl." Tibetan Buddhists consider the Medicine Buddha Empowerment to be the most powerful blessing for healing, dispelling sickness and for awakening the innate healing wisdom that lies within every individual.
The practice of the Medicine Buddha meditation (sadhana), and all the other ways of connecting to the blessings of the Medicine Buddha (such as those discussed on this page) are said to be much more effective when one has received the Medicine Buddha Empowerment (Tibetan: lung; Sanskrit: abisheka) from a qualified lama (Tibetan Buddhist meditation master).
  Medicine Buddha is one aspect of awakened mind, which the practitioner's (and the vajra master's) vast real unconditioned (non conceptual) mind. In this empowerment the lama reminds us, in a sense, of our deep innate connection with the Medicine Buddha.

The Art of Healing: A Tibetan Buddhist Perspective
"Thus, the distant causes of the diseases are seated in the past mental environment which was influenced by "afflictive emotions" -- mental factors that are the root cause of all illness. While these factors are impossible to enumerate, they are all the consequences of ignorance (Dhonden, p.15). Ignorance generates other negative states of mind such as desire, hatred, jealousy and pride. Such negative emotions drive our mentations, and our mentations contribute to our suffering."
"Understanding one's emotions is an essential part of the Buddhist journey to full awakening and freedom form unwanted conditions of all sorts. However, since most of us have very little ability to work with our emotional energies without creating negative experiences, medicines and other remedies are required."
"The Tibetan physician focuses his attention on spiritual factors even in the treatment of the simplest illnesses. Every Tibetan physician vows to 'regard medicine as an offering to the Medicine Buddha and all other medicine deities' and considers his 'medical instruments as holy objects' (Dummer, p. xix). Even the pharmaceuticals, which are mixtures of vegetable, animal and mineral compounds, are prepared with meticulous attention to religious ritual."
"One can also petition the healing powers of the Medicine Buddha by visualization practices .... Even the name of the Medicine Buddha is believed to have the power to free one from the pattern of negative thoughts and emotions. Healing can occur just by speaking, hearing or concentrating on his name. Thus, for example, conceited persons will become humble, greedy persons will become charitable and those who cause dissent will become cooperative and loving just by hearing or saying his name."
"Some examples of ritual involving the Medicine Buddha which are believed to have a curative or strengthening influence for the ill include meditating upon the deep blue color of lapis lazuli; making puja offerings of flowers and incense to the image of the deity; mentally or physically constructing an image of the deity; playing musical instruments and chanting; reading sutras; constructing altars, mandalas or banners; and lighting lamps."
  "The significance of the Medicine Buddha as the Supreme Healer in Tibetan medicine for liberating the individual from suffering is an exemplary metaphor for the mystical elements which are universally inherent in the healing tradition. The tradition is truly a holistic approach to the problem of suffering, both individual suffering and suffering as a universal condition."