Eligible treatment-seeking , cocaine-dependent subjects entered a @-week baseline period ( Phase I ) with high-value abstinence contingent vouchers and two motivational interviewing sessions , followed by a @-week medication trial ( Phase II ) with random assignment stratified on Phase I abstinence status to ( @ ) modafinil ( @mg/d ) , ( @ ) levodopa/carbidopa ( @/@mg/d ) , ( @ ) naltrexone ( @mg/d ) , or ( @ ) placebo .