Herbal therapy: an ancient and modern medicine for pain

Pain is an important defense reaction. Recurrent and persistent pain, though, is the most frequent font of sufference for humans. All civilizations, in the past and at the present, has looked to find methods of fighting pain. Many ancient cultures believed pain and disease were punishment for human folly and they tried to appease angry gods with rituals. After, herbal medicine has been one of the more developping way to try to control pain. The major part of the remedies that come from the past (even from millennia) has crossed the centuries and they still are advantageous, often with their derivatives, for obtaining analgesia. In this chapter, we discuss phytotherapeutic agents which are the more used for pain control, considering the historical aspects as well as the modern uses. In particular, we take into consideration the opium agents and the derivaties of Salix Alba, which both are progenitor of the most used analgesics (narcotic and non narcotic). Also, we consider the cannabinoids as old remedies which have interesting future perspectives in pain therapy. Finally, we reports on the ergot derivatives as an example of herbal agents which are used in particular pain conditions such as the primary headaches. Over one-third of the world's population suffers from persistent or recurrent pain (1), often associated with conditions such as back injury, migraine headaches, arthritis, herpetic and diabetic neuropathy, cancer. Chronic pain results not just from the physical insult but also from a combination of physical, emotional, psychological, and social abnormalities. Because many pains persist after an insult is healed, the ongoing pain rather than the injury underlies the patient's disability. Untreated pain may become self-perpetuating because pain has immunosuppressive effects that leave patients susceptible to subsequent diseases. It is now clear that if we can effectively treat the pain despite the underlying cause, it will be possible for patients to regain normal functioning. The key to more successful pain treatment is to understand the mechanisms that generate and perpetuate chronic pain. Major advances have occurred at levels spanning from molecular studies that have identified transduction proteins in nociceptors to cortical imaging studies which reveal how pain is experienced on a cognitive level (2,3). Two key lines of discovery have been molecular/cellular transduction mechanisms and neuronal plasticity. Since the beginning of the present century, theories of pain mechanism have evolved from specificity and summation models to the popular gate control theory. This latter pain theory, proposed by Melzack/Wall/Casey, has become the most important development in the field of pain management. Discoveries in recent years show that pain perception is no longer a straight forward afferent transmission of pain signal. It is a complex mechanism involving modulation coming from both peripheral and central nervous system. In the chronic pain state, pain signal generation can actually in the central nervous system without peripheral noxious stimulation. Anatomically, there are numerous ascending excitatory and descending inhibitory pathways in pain signal transmission. Centralization (cephalad relocation in the central nervous system) of the pain signal generators occur spontaneously or after these neural pathways are interrupted, leading to totally unexpected pain syndromes. Advanced reflex sympathetic dystrophy, deafferentation pain and phantom pain phenomenon are just a few examples. Traditionally, we suppose that pain is an important biological reaction of defense and a fortunate warning to put us on our guard against diseases. This may be true in disease states such as ap