The study, conducted between October 2003 and April 2005, enrolled 115 patients at an outpatient methadone clinic who met the criteria for cocaine dependence. About half (58) were randomized to receive the vaccine injections at weeks 0, 2, 4, 8, and 12 (the first injection marked week 0). Fifty-five of the 58 subjects randomized to the vaccine treatment completed all five injections. Maximum anticocaine concentration was reached between week 12 and week 16. The rest of the subjects received placebo in a double-blind manner.