Coadministration of MK-801 with amphetamine, cocaine or morphine prevents rather than transiently masks the development of behavioral sensitization.

Although coadministration of N-methyl-D-aspartate (NMDA) antagonists has been reported to prevent behavioral sensitization to psychomotor stimulants, it has been suggested that this effect is transitory and that sensitization is unmasked after longer periods of drug abstinence. To test this, rats were coadministered either amphetamine, cocaine, or morphine with the NMDA antagonist MK-801 and tested for sensitization after 7-10 days of abstinence. No sensitization was observed, suggesting that NMDA antagonists do not transiently mask sensitization but instead interfere with long-term processes responsible for its development.