Use of alcohol and other substances at the time of study enrollment and at subsequent study visits was assessed through multiple means including self-report, medical records, biomarker assessment, breathalyzer testing, urine toxicology screens, and collateral informant report. At each visit, the calendar-based Timeline Followback (TLFB)20 method was utilized to assess the frequency and amount of alcohol and drug use since the last visit. Breathalyzer testing (Alco-Sensor III®; Intoximeters, Inc., St. Louis, MO) and urine dipstick and confirmatory toxicology screens were conducted at each visit. State markers of heavy drinking such as liver function tests (gamma glutamyltransferase [GGT], aspartate aminotransferase [AST], and alanine aminotransferase [ALT]) and tests of mean corpuscular volume (MCV) were also conducted at each visit to provide an objective indication of alcohol relapse. Finally, collateral informant interviews were conducted as needed to determine relapse status in cases where participants were lost to follow-up or there was an indication that the participant may have used alcohol or other substances but the available evidence was conflicting.
