L-DOPA
Swedish scientist Arvid Carlsson first saw that the substance could be used as a drug, in  1957. It was first introduced as Madopar, by Hoffmann-La Roche, in 1973, as a treatment for Parkinson's disease. The WHO has put it on the list of essential medicines. Because the drug has side-effects, when taken for a longer period of time, people often try to replace it witrh other drugs, especially in younger patients.