**1. Introduction**

At the present time, many formulas for the relief of pain are present; among them, medicinal herbs are highlighted because of their wide popular use and availability. Many plant-derived compounds could offer valuable therapeutic effects for the treatment of chronic inflammatory conditions, which are likely associated with pain.

In the drug market today, about 40% of all medicines have been originated directly or indirectly from natural sources. It is estimated that about 25% being derived from plants, 13% from microorganisms and 3% from animals. For instance, morphine, salicin, artemisinin,

capsaicin, atropine, pilocarpine, digitalis, quinine, scopolamine and captopril are examples of drugs derived from natural sources [1, 2].
