First isolated in 1806 by German chemist. Disadvantage - physiologically addictive. Codeine - cough suppressant. Less addictive than morphine. Heroin is chemically modified from morphine.
Morphine acts on areas of brain involved with pain perception and accompanying anxiety.
A general nervous system depressant. Also used for diarrhea and cough suppression. Biologists were surprised that a plant chemical should have activity until they fed a rat radioactive morphine and found that its binds to specific sites. Have found opiate receptors in brain. Suggests that there must be internal opiates.