Chronic pain and cannabinoids. Great expectations or a christmas carol.

The discovery of the endocannabinoid system nearly three decades ago generated great interest among pain scientists. Moreover, its analogy with the opioid system in terms of evolutionary preservation, tissue localization and analgesic activity enabled a vast new field for the development of medicines addressed to those types of pain that still nowadays are difficult to manage. However, the main disadvantage that hampers the use of cannabinergic drugs as analgesics is their identification with recreational use, besides their psychotomimetic actions. Pain has traditionally been classified attending to the ailment duration (acute or chronic) and drugs are used according to the intensity of the pain to treat, but it is also important to target the mechanism involved despite the intensity or duration of pain. The present chapter reviews the study and use of cannabinoids attending separately to four classic types of pain: nociceptive, inflammatory, neuropathic and oncological, considering basic research (pain animal models) as well as clinical practice.