Backgrounds and Aims: Cinnamomum Zeylanicum is a medicinal herb used in Iranian traditional medicine as an analgesic spice, which its analgesic effect has been experimentally confirmed. Thus, this study was conducted to compare the antinociceptive effect of cinnamon essential oil (CEO) with those of Morphine and Diclofenac in mice.

Materials and Methods: 80 male albino mice were selected and randomly divided into 10 groups: a normal control group received distilled water, 3 test groups received different doses of CEO, 3 positive control groups were under the effect of different doses of Morphine Sulfate and another 3 positive control groups underwent the effect of 3 different doses of Sodium Diclofenac. Hot plate test was used to assess acute pain and writhing test was applied to measure the chronic pain.

Results: Hot plate test showed that response latency to painful heat and thereby the maximum possible effect was increased in groups receiving Morphine, Diclofenac and CEO as compared with the control group (p<0.05). In writhing test, Morphine, Diclofenac and CEO significantly reduced the severity of abdominal contractions in comparison with the control group. This pain relief in the group receiving 500 µg/ kg, of CEO at any time and for doses of 250 and 125 µg/ kg in the 2nd and 3rd periods was similar to groups receiving different doses of Morphine or Diclofenac.

Conclusions: Our findings concluded that CEO possesses antinociceptive properties. Its potency in chronic pain inhibition was similar to Diclofenac, thoughits acute antinociceptive effect was reported to be less than Morphine.