The Single Convention on Narcotic Drugs of 1961 is an international treaty to prohibit production and supply of specific (nominally narcotic) drugs and of drugs with similar effects except under license for specific purposes, such as medical treatment and research. As noted below, its major effects included updating the Paris Convention of 13 July 1931 to include the vast number of synthetic opioids invented in the intervening thirty years and a mechanism for more easily including new ones. From 1931 to 1961, most of the families of synthetic opioids had been developed, including drugs related to methadone, pethidine (meperidine/Demerol), morphinans and dextromoramide (Palfium, Palphium, Jetrium, Dimorlin, marketed solely in the Netherlands). Research on fentanyls and piritramide (R-3365, Pirium, Dipidolor, Piridolan, among others) was also nearing fruition at that point.