The British Medical Journal is launching a competition to decided the greatest medical breakthrough.
Present-day medical experts are championing discoveries from the last 166 years.
Trevor Turner, consultant psychiatrist at the Homerton Hospital, London is championing chlorpromazine.
Chlorpromazine was the first antipsychotic drug, used during the 1950s and 1960s.
ECT was used very widely before the introduction
Prior to its introduction, people with severe mental illnesses were given a range of treatments including electro-convulsive therapy (ECT) and sedatives such as bromide.
Chlorpromazine, a kind of antihistamine, was first tested as an anaesthetic on soldiers by French surgeon Henri Laborit in 1949.
He noticed patients became significantly calmer, and the drug's effect was confirmed when it was given to a man with mania a few years later.
Further trials followed, and by 1954 chlorpromazine was in use.
It was followed by the development of antipsychotics and antidepressants.
Dr Turner said: "Without the discovery of chlorpromazine, we might still have the miserable confinements witnessed by Montague Lomax [Experiences if an Asylum Doctor - 1921] - a world of desperate remedies.
"Then the attendant's role was akin to a zoo-keeper's; feeding, scrubbing and forcibly treating hundreds of 'demented' patients.
"It is hard not to see chlorpromazine as a kind of 'psychic penicillin', enabling patient and carer to communicate and transforming our understanding of human function."