Interactions Between Intravenous (IV) Cocaine and Lofexidine

Inclusion Criteria: * Be volunteers who meet Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (DSM-IV) criteria for cocaine abuse or dependence and are non-treatment seeking at the time of the study. * Be between 18 and 50 years of age, inclusive. * Be currently use cocaine. Use must be confirmed by a positive urine test for cocaine metabolites once within the outpatient screening period. * Be able to verbalize understanding of the consent form and provide written informed consent. * Females must have a negative pregnancy test within 72 hours prior to receiving the first infusion of cocaine. They must also be postmenopausal, have had a hysterectomy, been sterilized, or agree to use one of the following methods of birth control: * diaphragm and condom by partner * intrauterine device (that does not contain progesterone) and condom by partner * sponge and condom by partner * complete abstinence from sexual intercourse Note: Oral contraceptives, Depo-Provera, Norplant, Patch, and intrauterine progesterone contraceptive system are not allowed. Exclusion Criteria: * Please contact site for more information