“…Similarly, studies of volunteers suggest that they can contribute to the enhancement of treatment and long-term recovery outcomes (Bassuk, Hanson, Greene, Molly, & Laudet, 2016;Reif et al, 2014). Volunteer service to others in mutual support groups has also been associated with increased engagement with treatment, improved treatment retention, and/or decreased alcohol and other drug use (Boyd et al, 2005;Dembo, Wothke, Livingston, & Schmeidler, 2002;Grant, Ernst, Streissguth, Phipps, & Gendler, 1996;Lee, Pagano, Johnson, & Post, 2016;Leigh, Hodgins, Milne, & Gerrish, 1999;Pagano, Friend, Tonigan, & Stout, 2004;Stahler et al, 2007;Zemore, Kaskutas, & Ammon, 2004). Additional detailed background and description of volunteers in substance use care is provided in a companion paper (Passetti et al, under review).…”