An experimental drug that relieves pain like morphine but is not addictive showed promise in a study of mice, the Los Angeles Times reports. Stanford University researchers gave one group of mice the compound, called PZM21. A second group was given morphine. Both groups of mice were placed on a hot surface. PZM21 offered almost as much pain relief as morphine, and lasted for up to three hours—substantially longer than morphine, the researchers report in the journal Nature . Mice given PZM21 were no more likely to return to a place where they got the drug than to a similar chamber that offered a saline solution. This indicates the mice did not find the compound addictive, the researchers noted.