Our study shows that in Tehran, patients receiving MMT predominantly used opium and crystalline heroin, whereas other drugs were the main drugs for only a minority of MMT patients. Generally, the clear majority of participants receiving MMT were young, educated, married, and employed men.
According to the world drug report, in 2009, between 149 and 272 million people between the ages of 15 and 64 consumed illegal drugs, of whom about 10% to 20% were considered dependent and regular drug users . Patterns of drug dependency vary across countries: Iran, with more than one million regular drug users, has the world’s highest rate of dependence on opiate drugs [3, 4].
Tehran, as the capital of Iran and with a population exceeding 12 million, comprises a considerable section of the population. This study was conducted on MMT patients of private outpatient treatment centers in Tehran. Because public centers are so few, our sample provides a good overview of patients participating in MMT programs. MMT is the main treatment for opiate users available at official outpatient medical addiction treatment centers; consequently, this sample sheds light on the majority of opiate addiction treatment seekers who were referred to this official network.
Opium seems still to be the drug of choice among Iranian addicts given that most studies in Iran acknowledged the higher frequency of addiction to opium than to other drugs [6, 8]. Our results are similar to the findings of a previous study of a group of drug addicts seeking treatment in a general practice in Shiraz, which reported opium and heroin as the drugs most commonly abused . The most recent Iranian rapid situation assessment of drug abuse in 2007 reported opium, crystalline heroin, and heroin to be the three most prevalent drugs previously abused by those attending treatment centers and in the general population . Similar findings have also been reported in a multi-center study of seven outpatient centers in four Iranian cities . The high prevalence of the history of opium use in our study compared to the estimates in the World Drug Report 2011 might be due to seeking treatment or less stigmatized self-report of using opium instead of heroin . Only 1% of the patients reported amphetamines as their main drug of abuse, but as many as 15% reported using this drug for at least one month in their lifetime prior to treatment. Since amphetamines are easily available in the Iranian drug market in comparison with other stimulants like cocaine , and that they may alleviate some of methadone side effects, they can cause a serious threat for the treatment process in the MMT clinics in Iran.
Crystalline heroin users were younger than opium users, and most of them had begun using drugs at younger ages. Moreover, the duration of addiction among crystalline heroin users tended to be shorter than among opium users. The amount of money most of the participants had spent on drugs was higher than the monthly MMT fee in these clinics (i.e. USD 80–90). This monthly treatment fee consists of a small proportion of the average monthly income of an urban family in Tehran http://www.cbi.ir. Crystalline heroin users had spent more money on their drugs during their last month of addiction than had opium addicts. Although a majority of the participants reported being under some kind of treatments earlier, most of them were receiving MMT for the first time. Overall, about 60% of the patients had been in MMT for more than six months. The mean daily dose of methadone among crystalline heroin users was higher than among opium users, but, it was in the recommended range of 60 to 120 mg [14–16]. Although the mean daily dose of methadone was in the recommended range, as much as 30% of the patients received up to 30 mg methadone. In Iran, methadone is usually prescribed in syrup or tablet forms. In our study the proportion of methadone in syrup and tablet forms among the MMT patients was about the same.
In line with previous findings, drug abuse is strongly related to male gender, particularly in the Eastern Mediterranean region [17–21]. Little is known about female addicts in the Middle East, and no comprehensive study on the prevalence of drug abuse among Iranian women exists. Consequently, it is unclear whether the low proportion of female participants in our study was due to a limited number of female addicts in general or their reluctance to seek professional help in treatment centers. Possible reluctance of women to give their consent to participate in the study was unlikely since the response rate among female participants (74%) was close to the overall response rate (72%).
In our study, most of the patients receiving MMT were fairly young. This is in line with a study by Day et al.  of drug abusers in a general practice in Shiraz, Iran. Another report of drug abuse among the general population in Kerman, however, found no significant association between drug abuse and age group . Studies in other countries also show a higher prevalence of addiction among young people [17, 18, 21, 22].
In contrast with other studies of general populations that reveal lower rates of addiction among more educated people [6, 23], most of the MMT participants in our study had more than elementary school education. A study of drug abuse in Thailand reported somewhat similar findings among addicts in rural areas . As a review article by Mokri  emphasized, most of the participants attending treatment centers in our study were also employed. Similar results emerged in another study of opioid-dependent patients seeking treatment in a major center in Shiraz . In contrast, another study of opium use in a rural area of Iran found a significant association between opium use and unemployment . On the other hand, in a population-based study of opium use in Fars province, opium use cut across all employment status groups . The differences between the profile of MMT patients in our study and other studies in similar settings with general population of addicts reflect the diversity of the patients in terms of their socioeconomic status including education and employment. This indicates that in-treatment patients may be of higher socioeconomic level and may have more resources than the other addicts.
Bearing in mind that this study was a cross-sectional survey of patients attending outpatient addiction treatment centers, no causal inferences of underlying factors can be outlined. In addition, the findings from patients in MMT cannot be generalized to the whole population of drug users. One limitation of the study is that because of practical reasons only eight clinics were included in the study. Although the data are based on patients’ self-reported addiction history, we tried to decrease the likelihood of underreporting via good collaboration with the clinic staff. However, it has to be kept in mind that tendency towards “social desirability” among clients in a good therapeutic alliance to caregivers can be a source of under-reporting. This limitation is true for all studies regarding drug abuse history.
Despite these limitations, our study has several strengths. The stratified random sampling method outlined well patients seeking treatment in addiction treatment centers from all three main socioeconomic areas of the city. In addition to the broad coverage, the large sample size along with the high response rate in this marginalized target group bolsters the reliability of the results in this capital city of more than 12 million. It is worth mentioning that our response rate of 72% may be somewhat low, as it is based on the number of study participants among the total monthly turnover in the clinics, rather than on the number of patients asked to participate. Furthermore, by utilizing a structured interview instead of a self-administered questionnaire, we reduced the possibility of misunderstandings in this compromised group.
Our study provides valuable information about the characteristics of patients attending addiction treatment centers in Iran. Although Tehran represents a considerable proportion of the Iranian population, a national survey of all drug abusers would be necessary to obtain a more thorough understanding of the predisposing factors associated with illegal drug abuse.