Dextromethorphan Effects on Hyperalgesia: Using the freeze-injury pain model in a randomized, double-blind, placebo-controlled crossover trial of 30-mg doses of oral dextromethorphan in 20 male volunteers, dextromethorphan was antihyperalgesic and reversed peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-d  aspartate receptors may need to be sensitized by pain for dextromethorphan to be effective.