As shown in Figure 1, morphine could alleviate both of phases, whereas Leonurus cardiaca at dose of 250 mg/kg diminished only the formalin-induced pain of the late phase.
Demonstrating in Figure 1, Leonurus cardiaca extract only at the maximum administrated dose (500 mg/kg) was capable of reducing the formalin-induced pain in the early phase, and other doses (125 and 250 mg/kg) did not show such effect.
Treating the animals with Leonurus cardiaca, at dose 500 mg/kg, alters mouse latency to painful thermal stimulus in tail flick and hot plate tests.
In this study, it was shown that the administration of ethanolic aerial part extract of Leonurus cardiaca possesses antinociceptive effects in tail flick, hot plate, and both phases of formalin test.
Hofmann, "Bitter substances from labiate plants: a clerodane derivative from Leonurus cardiaca," Tetrahedron Letters, vol.