Cocaine-Methylphendidate Interaction Study - 4

Inclusion Criteria: 1. male or female of any race, between 21 and 45 years of age. 2. cocaine dependent according to DSM-IV criteria. 3. currently use cocaine by smoked or intravenous route of administration and confirmed by positive urine screen for benzoylecgonine within 2 weeks prior to signing the informed consent form. The subjects who currently use cocaine by smoked route must have a history of intravenous exposure to drugs of abuse. 4. in stable physical and mental health as judged by interview and physical examinations. 5. for female subjects, test non-pregnant and use adequate birth control. All female subjects will have a serum pregnancy test performed prior to the first dose of study medication. 6. be capable of providing written informed consent to participate in this study. 7. able to comply with protocol requirements and be likely to complete all study treatments. 8. within 20% of ideal body weight. Exclusion Criteria: 1. require detoxification from alcohol, opiates, or sedative-hypnotics. 2. have a history of significant hepatic, renal, endocrine, cardiac (i.e., arrhythmia requiring medication, angina pectoris, myocardial infarction), stroke, seizure, neurological, non-drug-related psychiatric, gastrointestinal, pulmonary, hematological or metabolic disorders. 3. have a history of adverse reaction to cocaine including loss of consciousness, chest pain, psychosis, or seizure. 4. have a history of adverse reaction/hypersensitivity to methylphenidate. 5. test positive upon urine toxicology screen for opiates, benzodiazepines, barbiturates or related CNS depressants, amphetamines or related stimulants. 6. have clinically significant abnormal laboratory measurements in liver function tests (AST and ALT levels greater than 3 times of the upper limit of normal), hematology (CBC, differential, platelet count), serum chemistries (SMA-24) and EKG. 7. have any significant active medical, or psychiatric illness which might inhibit their ability to complete the study or might be complicated by administration of the test drug. 8. have active hypertension as defined by the American Heart Association criteria. 9. currently receive any medications for the treatment of any significant medical conditions. 10. have a history of glaucoma. 11. have a diagnosis or family history of Tourettes syndrome. 12. have an abnormal thyroid function (as determined by an abnormal T4 level). 13. have a history of seizures or seizure disorder. 14. have any medical history or condition considered by the investigator(s) to place the subjects at increased risk.