Opiates, originally derived from the opium poppy, have been used for thousands of years for both recreational and medicinal purposes. The most active substance in opium is morphine - named after Morpheus, the Greek god of dreams. Codeine, a less powerful drug, is also found in opium. Both these opiates relieve pain, relax muscles and cause drowsiness. All opiates mimic your body's own painkillers. Morphine is a very powerful painkiller, but it is also very addictive.