How Do Painkillers Find & Kill Pain?

"First, we need to make a distinction between the two main classes of painkillers, which are used for different situations and function via different mechanisms.The first class is the narcotic opioid drugs. These are the heavy-duty drugs, like morphine and codeine, used to treat severe pain. They relieve pain in two ways: first by interfering with and blocking the transmission of pain signals to the brain, and then by working in the brain to alter the sensation of pain."

[via mental floss]