Analgesic effects of eucalyptus essential oil in mice.

Background: The use of aroma oils dates back to at least 3000 B.C., where it was applied to mummify corpses and treat the wounds of soldiers. Since the 1920s, the term "aromatherapy" has been used for fragrance therapy with essential oils. The purpose of this study was to determine whether the essential oil of Eucalyptus (EOE) affects pain pathways in various pain conditions and motor coordination.

Methods: Mice were subjected to inhalation or intraperitoneal injection of EOE, and its analgesic effects were assessed by conducting formalin, thermal plantar, and acetic acid tests; the effects of EOE on motor coordination were evaluated using a rotarod test. To determine the analgesic mechanism, 5'-guanidinonaltrindole (κ-opioid antagonist, 0.3 mg/kg), naltrindole (δ-opioid antagonist, 5 mg/kg), glibenclamide (δ-opioid antagonist, 2 mg/kg), and naloxone (μ-opioid antagonist, 4, 8, 12 mg/kg) were injected intraperitoneally.

Results: EOE showed an analgesic effect against visceral pain caused by acetic acid (EOE, 45 mg/kg); however, no analgesic effect was observed against thermal nociceptive pain. Moreover, it was demonstrated that EOE did not have an effect on motor coordination. In addition, an anti-inflammatory effect was observed during the formalin test.

Conclusions: EOE, which is associated with the μ-opioid pain pathway, showed potential effects against somatic, inflammatory, and visceral pain and could be a potential therapeutic agent for pain.