BackgroundCo-use of heroin kerack with methamphetamine (MA) is a new epidemic health concern among Iranian female drug users. Yet, little is known about this issue because of stigma.ObjectivesThe current study aimed to investigate the reasons associated with initial and continued co-use of heroin kerack with MA among two groups of regular and recreational female co-users, their motivations associated with treatment entry and to compare their general characteristics at a drop in center (DIC) in Tehran.Materials and Methods82 clients were randomly recruited. A researcher-designed questionnaire was used to collect data. Data was analyzed by performing descriptive statistics, the Chi-square test and t-test.ResultsThe mean age of the participants were 31 (SD = 8) years. Reducing negative affect (55%), addicted family and social networks (50%), curiosity (48%), and the lack of knowledge on addictive effects of co-use of heroin kerack with MA (32%) were the most frequently reported reasons at initiation. Drug dependence (71%) and drug availability (56%) were reasons of continued co-use. Restoring health (61%), fear from becoming MA abuser only (33%), and fear from making a transition from heroin kerack and MA smoking to injection (15%) were important motivations for treatment entry. Regular co-users were more likely to be single (41.7% vs. 14.7%, P < 0.001), jobless (45.8% vs. 38.2, P < 0.05), homemaker (50% vs. 35.3%, P < 0.01), recently incarcerated (16.7% vs. 11.7%, P < 0.01), and were less likely to be enrolled in opioid replacement programs (33.5% vs. 41%, P < 0.01). Regular co-users were younger (30.6 vs. 32.1 years, P < 0.05), less educated (9.6 vs. 10.8 years, P < 0.05) and had a longer duration of drug dependence (9.6 vs. 8 years, P < 0.05).ConclusionsReasons associated with initial and continued co-use of heroin kerack with MA, factors associated with treatment entry and the differences between regular and recreational co-users should be specifically considered in designing and tailoring drug use treatment programs for this group.