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In their recent article, van Gorp et al¹ did not specify whether they excluded subjects who met DSM-IV criteria for nicotine dependence. Although subjects were administered a urine screen to examine for substances of abuse, cigarette smoking status was apparently not assessed. Nicotine dependence and withdrawal were considered important confounding factors in a previous study exploring the relationship between hand tremor, frequency of cocaine use, and duration of cocaine abstinence.² Nicotine has been observed to reduce the tremor of parkinsonism but increase physiologic tremor,³ either of which could have significantly affected the results obtained by van Gorp et al¹ on the timed Pursuit Rotor Task. Nicotine stimulates release of dopamine by presynaptic and postsynaptic actions on dopaminergic neurons,³ so alterations in the dopamine system and performance on tasks of psychomotor function in subjects who were dually cocaine- and nicotine-dependent might result from exposure and/or withdrawal from either substance.

If nicotine . . . [Full Text of this Article]