 3. 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. 