Participants
schizophrenia, opioid use disorder, bipolar disorder, psychosis
The statistical population included adult patients with opioid use disorder undergoing MMT. The inclusion criteria in this study were the willingness to participate, age over 18, literacy, drug use confirmed by positive urine tests, taking methadone as supervised by a physician for at least three months, and no chronic mental illnesses, such as psychosis, bipolar disorder, and schizophrenia. As well the exclusion criteria were the participants’ decline to continue the study for any reason, changes to the treatment plan, and the use of zinc-containing compounds prior to the intervention program.The sample size was thus estimated at 32 individuals in each group, with reference to a similar study with 80% test power and a 95% confidence interval. Considering the 20% sample loss, the final sample size in each group was determined to be 40. The researcher then referred to the selected addiction treatment clinic for the sampling of the convenience type. For this purpose, first, the patients with opioid use disorder undergoing MMT were examined in terms of meeting the inclusion criteria. Next, the study objectives and phases, data confidentiality, and the voluntary basis of entering into and withdrawing from the research process were presented by holding face-to-face meetings with the eligible individuals. Afterward, those who agreed to participate in the study signed an informed consent form. Finally, out of 140 patients with opioid use disorder referred to the addiction treatment clinic concerned, 100 individuals with a history of at least three months of receiving methadone met the inclusion criteria, of which 80 ones agreed to participate in the study. A randomized block design was further utilized to allocate the samples to the intervention and control groups. The random allocation sequence (with 20 blocks of four) was accordingly established using the Random Allocation Software. For the act of concealment, some closed envelopes containing cards with the letters A (for the intervention group) and B (for the control group) were prepared according to an encoded allocation sequence. An envelope was then opened by an outsider who had no role in the study and did not know about the card inside for each individual. Based on the card inside, the patients with opioid use disorder were allocated to one of the intervention or control groups. Of note, only the data analyst was blinded to the allocation of the participants to the groups in this study to ensure that all the analytical decisions were made without bias. The CONSORT flow diagram of the study is illustrated in Fig. The research process according to the CONSORT flow diagram (2010)