The buprenorphine group reduced the number of days of illicit opioid use per week from 5.4 days ( 95 % CI , 5.1-5 .7 ) to 0.9 days ( 95 % CI , 0.5-1 .3 ) vs a reduction from 5.4 days ( 95 % CI , 5.1-5 .7 ) to 2.3 days ( 95 % CI , 1.7-3 .0 ) in the referral group and from 5.6 days ( 95 % CI , 5.3-5 .9 ) to 2.4 days ( 95 % CI , 1.8-3 .0 ) in the brief intervention group ( P < .001 for both time and intervention effects ; P = .02 for the interaction effect ) .