“…The screening process identified 21 studies reported in 22 papers (see Figure 1 for PRISMA flow diagram (33)). Most were carried out in the USA (n=16) (34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50), with two in Australia (51,52) and one in each of Switzerland, Taiwan and UK (53)(54)(55). 11 studies included only service users (34, 35, 37, 40, 44-46, 50, 51, 54, 55), five only treatment providers (41,42,47,48,52), and five both (36,38,39,43,49,53).…”