The buprenorphine group reduced the number of days of illicit opioid use per week from @ days ( @ % CI , @-@ @ ) to @ days ( @ % CI , @-@ @ ) vs a reduction from @ days ( @ % CI , @-@ @ ) to @ days ( @ % CI , @-@ @ ) in the referral group and from @ days ( @ % CI , @-@ @ ) to @ days ( @ % CI , @-@ @ ) in the brief intervention group ( P < @ for both time and intervention effects ; P = @ for the interaction effect ) .