Although for the full 16 weeks cocaine positive urine rates showed no significant difference between the three groups ( placebo , high , low IgG ) , after week 8 , more vaccinated than placebo subjects attained abstinence for at least two weeks of the trial ( 24 % vs 18 % ) , and the high IgG group had the most cocaine-free urines for the last 2 weeks of treatment ( OR = 3.02 ) , but neither were significant .