The majority of studies were conducted in the United States (k = 7, 54%), with the remaining studies conducted in the United Kingdom (k = 3, 23%), Canada (k = 2, 15%) and Australia (k = 1, 8%) (Table 1). Most of the studies (k = 10, 83%) were published after the year 2000. Because the studies targeted different levels of stigma, the sample sizes varied substantially, ranging from 28 to 445 (median = 108). Eleven studies (85%) used quantitative methodological approaches, including self-report survey methods in 10 (77%) studies. Three studies (23%) assessed stigma beyond the immediate post-intervention period, including a 35-day [60], 90-day [61] and 12-month [67] follow-up. Whereas the majority of studies (k = 7, 54%) were not focused on specific types of substances, the remaining interventions focused on alcohol only (k = 3, 23%), alcohol and specific drugs (e.g. cocaine) (k = 2, 15%) and injection drug use (k = 1, 8%). All the studies were restricted to adult populations.
