The MI group reported 3.5 fewer days of alcohol use ( 2.1 versus 5.6 days ; 95 % CI = -6.5 to -0.6 ; P = 0.020 ) and 4.0 fewer days of drug use ( 3.8 versus 7.8 days ; 95 % CI = -7.5 to -0.4 ; P = 0.028 ) ; however , abstinence rates and severity scores did not differ between conditions .