Morphine (INN) (IPA: [ˈmɔ(ɹ)fin]) is a highly potent opiateanalgesicdrug and is the principal active agent in opium and the prototypical opiate. Like other opiates, e.g. diacetylmorphine(heroin), morphine acts directly on the central nervous system(CNS) to relievepain, and at synapses of the nucleus accumbens in particular. Studies done on the efficacy of various opioids have indicated that, in the management of severe pain, no other narcotic analgesic is more effective or superior to morphine. Morphine is highly addictive when compared to other substances, and tolerance, physical and psychological dependences develop very rapidly.

*source www.Wikipedia.org and http://workplace.samhsa.gov/Glossary/glossary.aspx