Pain is the chief reason that people seek medical care. And whether it is a tooth, ear, stomach, head, or back that aches, people all want the same thing--relief. Since ancient times, humanity has been preoccupied with finding ways to relieve pain. For thousands of years, our ancestors had only a few substances (mainly alcohol, opium, and the coca and hemp plants) to help make the pain go away.

But modern pharmacology changed all that. Today, dozens of drugs mercifully eliminate, or at least greatly reduce, the pain that comes with all types of ailments. However, their effectiveness for chronic pain is a different matter. Treating chronic pain is tricky; great care and caution must be exercised because of the potential for side effects and addiction associated with pain-relieving drugs.