Charles P. O'Brien (born August 20, 1939, New Orleans, Louisiana) is a research scientist, medical educator and a leading expert in the science and treatment of addiction.

In the US, O'Brien has chaired or served as a member of many Institute of Medicine committees dealing with science and drug abuse policy matters.

[2] The purpose of this committee was to revise the primary classification system, known as DSM-5, that psychiatrists use in diagnosing mental illnesses, including addiction disorders.

Based on animal studies, O'Brien in the 1980s theorized that alcohol produced pleasure by releasing endorphins – the brain's naturally occurring opioids.

[9] Individuals with a particular genetic variant have a sensitive endogenous opioid system that is activated by alcohol, thereby producing stimulation and euphoria.

O'Brien and his colleagues never applied for a patent on the discovery of naltrexone's effectiveness for treating alcohol addiction, so this treatment continues to be used at no cost worldwide.