3.1 Follow-up sample
Of the 73 who were exposed to their study treatment, 60 were followed at least once. There were no significant differences by condition in rates of follow-up, data availability or length of time covered during the follow-up (mean 154.4 days for CBT4CBT and 146.6 for TAU, F(1)=0.51, p=.48). One participant in the TAU condition died during the follow-up period. There were no significant differences between those who were reached for follow-up and those who were not reached in terms of baseline demographic or substance use related variables. However, compared to the 60 participants reached for follow-up, the 13 participants not reached had completed significantly fewer weeks of the study protocol (6.1 versus 4.1, F(1)=8.8, p=.004)
3.2 Treatment involvement during follow-up
During the six month follow-up period, 38% of those reached received some psychiatric treatment, 75% received some form of substance abuse treatment, and 12% had been arrested. However, intensity of involvement in any of these activities was fairly low, as participants reported they attended an average of 2.3 days of outpatient drug treatment, 1.5 days of inpatient treatment, and 5.8 days of self-help per month, and less than one day of any psychiatric treatment per month with no significant differences in the in the frequency or intensity of these events by treatment condition.
3.3 Relationship of within treatment outcomes to substance use during follow-up
As expected, there were fairly strong and consistent relationships between within-treatment substance use and outcome during the follow-up. For the sample as a whole, the percentage of drug-negative urine specimens collected during treatment was significantly correlated with the longest period of consecutive abstinence during follow-up (r=.42, p<.01). Similarly, those who attained longer consecutive periods of abstinence within treatment had significantly longer periods of abstinence during follow-up (r=.55, p<.01). For the participants randomized to CBT4CBT, the number of CBT4CBT modules started had a significant positive relationship with maximum days of abstinence during the follow-up (r=.49, p=.02).
3.4 Drug use during follow-up by treatment condition
As shown in , which presents estimated means of days of drug use by month by treatment, those assigned to CBT4CBT tended to continue to reduce their drug use slightly across the follow-up period, while those assigned to TAU tended to increase their frequency of drug use. Random effects regression analysis indicated no significant effects for group (t= 0.1, p=.92) or time (t=.70, p=.48), but a significant group by time effect (t=2.2, p=.03). When treatment retention (‘days retained in treatment’) was added to the model as a covariate, the covariate was significant (t=−3.2, p=.003) and indicated that overall, participants who were retained in protocol treatment reported fewer days of drug use during follow-up. The group by time effect remained significant (t=2.3, p=.025) suggesting that the sustained improvements following CBT4CBT compared with TAU remained significant even after accounting for treatment exposure. Similarly, when maximum consecutive duration of abstinence was added to the model, the covariate was again significant (t=−2.9, p=.005) indicating overall better outcome during follow-up for those participants who had achieved longer periods of abstinence within the 8-week treatment period. The group by time effect remained significant as well (t=2.4, p=.015). Finally, when ‘total days of substance abuse treatment during follow-up’ was added to the same model as a covariate, the covariate was not significant, indicating that level of exposure to substance use treatment during follow-up was not strongly associated with drug use outcomes during this period. Again, the group by time effect favoring CBT4CBT over TAU remained statistically significant even after controlling for exposure to treatment (t=2.2, p=.03).
Days of any drug use by month (treatment endpoint to end of 6-month follow-up) and treatment condition, estimates from random regression analyses
presents results of urine toxicology screens and self-reported drug use and results of urine toxicology screens at each follow-up by treatment condition. Across groups, participants reported they were abstinent for 84% of days throughout the follow-up, but group differences were not statistically significant. Those assigned to CBT4CBT reported a significantly higher period of consecutive abstinence from all drugs during the follow-up period (102 versus 72.5 days, F=3.9, p=.05). Moreover, those assigned to CBT4CBT were significantly more likely to submit a drug-negative urine specimen at the 1 month follow-up (76% versus 48%, F=3.9, p=.05). At the 3-month and 6-month follow-ups, those assigned to CBT4CBT submitted a higher proportion of drug-free urine specimens, although the difference was not statistically significant at these points.
Substance use outcomes during follow-up by treatment condition