It's actually not that uncommon. There is that phenomena that psych inpatients want a pill...ANY pill, when they want one. If they can get a thorazine PRN, they'll take it. These patients can be tough to deal with. Some will even take PRNs of Tylenol, which is not benign either. Sometimes the tranquilizing effect of thorazine is appealing to patients.
Hell, you can buy zyprexa and seroquel on the street now...about $15 a bottle from what I hear.