Dose-dependent antinociceptive effects produced by morphine, oxymorphone and <i>N</i>-methylmorphinans 1, 4 and 6.

<p>(A) Hot-plate test. (B) Tail-flick test. Hot-plate and tail-flick latencies (as %MPE) are shown at 30 min (peak of action) after s.c. drug administration to mice. Data are shown as the mean ± SEM (<i>n</i> = 5–6 mice per group).