Repeated drug consumption may progress to problematic use by triggering neuroplastic adaptations that attenuate sensitivity to natural rewards while increasing reactivity to craving and drug cues. Converging evidence suggests that glutamate modulation may work to correct these adaptations and rapidly restore motivation for delayed non-drug rewards relative to immediate drug use. Using an established laboratory model aimed at evaluating behavioral shifts in the salience of cocaine now vs. money later, the investigators will test the effect of CI-581a on cocaine self-administration as compared to the active control.

Inclusion Criteria:

1. Active cocaine dependence with at least 8 days of use or at least 4 binges of large amounts (>$200/occasion) over the past 30 days, and displaying at least one positive utox during screening
2. Physically healthy
3. No adverse reactions to study medications
4. 21-55 years of age
5. Capacity to consent and comply with study procedures, including sufficient proficiency in English
6. Not seeking treatment

Exclusion Criteria:

1. Meets DSM IV criteria for current major depression, bipolar disorder, schizophrenia, any psychotic illness, including substance induced psychosis, and current substance-induced mood disorder with HAMD score > 12.
2. Physiological dependence on another substance, such as alcohol, opioids, or benzodiazepines, excluding caffeine, nicotine, and cannabis
3. Delirium, Dementia, Amnesia, Cognitive Disorders, or Dissociative disorders
4. Current suicide risk or a history of suicide attempt within the past year
5. Pregnant or interested in becoming pregnant during the study period
6. Any of the following cardiac conditions: clinically significant left ventricular hypertrophy, angina, clinically significant arrhythmia, or mitral valve prolapse
7. Unstable physical disorders which might make participation hazardous such as end-stage AIDS, hypertension (>140/90), WBC < 3.5, active hepatitis or other liver disease with elevated transaminase levels (< 2-3 X upper limit of normal will be considered acceptable if PT/PTT is normal), renal failure (creat > 2, BUN >40), or untreated diabetes
8. Previous history of ketamine or midazolam misuse or abuse, and a history of an adverse reaction/experience with prior exposure to cocaine, ketamine or midazolam
9. Recent history of significant violence (past 2 years)
10. Abnormal pseudocholinesterase level
11. First degree relative with a psychotic disorder (bipolar disorder, schizophrenia, schizoaffective disorder, or psychosis NOS)
12. BMI > 35, or a history of documented obstructive sleep apnea
13. On psychotropic or other medications whose effect could be disrupted by participation in the study

6 weeks.