“…One showed positive results (Silverman, Svikis, Robles, Stitzer, & Bigelow, 2001) and one showed negative results (Knealing, Wong, Diemer, Hampton, & Silverman, 2006). One study (Holtyn, Koffarnus, DeFulio, Sigurdsson, Strain, Schwartz, & Silverman, 2014; Holtyn, Koffarnus, DeFulio, Sigurdsson, Strain, Schwartz, Leoutsakos et al, 2014), designed to promote abstinence from both opiates and cocaine in adults who were out-of-treatment and injected drugs, arranged employment-based reinforcement for participants enrolled in the Therapeutic Workplace first for enrolling in methadone treatment; then for providing urine samples every Monday, Wednesday and Friday that were negative for opiates; and then for providing urine samples that were negative for opiates and cocaine. The study showed that the sequential application of abstinence reinforcement contingencies was effective in promoting abstinence from opiates and cocaine.…”