 In the early 1950s, methadone (most times the racemic HCl salts mixture) was also investigated for use as an antitussive.Isomethadone, noracymethadol, LAAM, and normethadone were first developed in Germany, United Kingdom, Belgium, Austria, Canada, and the United States in the thirty or so years after the 1937 discovery of pethidine, the first synthetic opioid used in medicine.These synthetic opioids have increased length and depth of satiating any opiate cravings and generate very strong analgesic effects due to their long metabolic half-life and strong receptor affinity at the mu opioid receptor sites.