Opiates have been used medically since ancient times and it ranks as one of the most effective pain-relieving drugs. There are over two dozen opiate alkaloids such as Papaver somniferum, Papaver paeoniflorum, and Papaver rhoeas. The active principles of opium reside in its alkaloids, the most important part which is morphine. Opium alkaloids are of two types. One type; Morphine, codeine, and thebaine, act upon the nervous system. They are analgesic, narcotic, and potentially addicting compounds. The other type; Papaverine, noscapine and most of the other opium alkaloids are not analgesic, narcotic, or addicting; instead they act to relax involuntary (smooth) muscles.

For many years morphine was the physician's mainstay for the relief of severe pain, although powerful synthetic substitutes have now partially replaced it. Codeine is used for relieving coughs and other conditions not so painful as to require morphine. Thebaine has no medical value itself except for manufacturing codeine.

In the treatment of pain, the opium alkaloids are given orally, rectally, or by injection. Opium is used orally in the form of its alcoholic tincture for the treatment of diarrhea. The medical needs of the world exceeded 1,700 tons by the 1980's in spite of the advent of synthetic drugs that often can be substituted for opium.