title: Endorphins and on-demand pain relief.
mesh_terms: D000698:Analgesia / Q000379:methods; D004723:Endorphins / Q000008:administration & dosage* / Q000134:cerebrospinal fluid; D006801:Humans; D008614:Meperidine / Q000008:administration & dosage*; D010146:Pain / Q000188:drug therapy*; D012646:Self Administration / Q000295:instrumentation
chemical_list: D004723:Endorphins; D008614:Meperidine