<qa>  What is the effect of AChE inhibition on plasma levels of cocaine and cocaine metabolites3. To determine the effects of AChE inhibition on plasma levels of cocaine and cocaine metabolites. Hypothesis 3A. Relative to placebo-treated participants, treatment with rivastigmine, but not HupA, will be associated with increased plasma levels of cocaine. Hypothesis 3B. Relative to placebo-treated participants, treatment with rivastigmine, but not HupA, will be associated with increased formation of ecgonine and benzoylecgonine, and decreased formation of ecgonine methylester. 