OBJECTIVE: Impulsivity is a transdiagnostic risk factor for numerous health morbidities and is strongly associated with early relapse and poor treatment outcomes in addictions and mood-disorders. Lithium carbonate can be helpful in moderating the impulsive behaviors associated with mania, possibly mediated by reduced myo-inositol activity following inhibition of the enzyme inositol monophosphatase (IMPase). We tested the hypothesis that impulsivity-as motor disinhibition, decisions without adequate information, and stronger preferences for small immediate rewards over larger later rewards-can be moderated by the IMPase inhibitor ebselen in healthy adult volunteers. METHODS: One hundred and thirty healthy adults completed a between-subjects, double-blind, placebo-controlled protocol. Over 2 days, participants received a previously validated dose of 1800 mg of ebselen or placebo before completing tests of impulsivity and decision-making. RESULTS: There were no substantive changes in any measure of impulsivity following treatment with ebselen compared with placebo. Neither was there any convincing evidence of stronger treatment effects in high-trait impulsive participants compared with low-trait participants. CONCLUSION: These results fail to replicate findings that ebselen administration moderates validated measures of impulsivity in healthy adults, at least at doses shown to reduce myo-inositol within the medial prefrontal cortex and produce changes in emotional processing and reward-based learning.