Daily repeated administration of methamphetamine (MAP) developed reverse tolerance to its ambulation-accelerating effect. After pretreatment of mice daily with ginseng extract (GE) for 5 days, concomitant injections of MAP and GE suppressed the development of reverse tolerance to the effect of MAP, although GE itself did not affect the spontaneous motor activity of the naive mice. These results provide evidence that GE may be useful for prevention and therapy of the adverse action of MAP.