 - Current use of cocaine, amphetamine, phencyclidine, or ketamine, documented either by history or by urinary drug screening at Screening and Baseline Visits. Urinary drug screening for ketamine and phencyclidine will conducted off-site by the Study Sponsor if urinary drug screening available at the study site does not include these drugs. Any other drugs identified incidentally on drug screening will warrant exclusion only if the Principal Investigator, in consultation with the Sponsor, judges that their presence could interfere with the objectives of the trial. 