Introduction
Estimations of the prevalence of opiate use in the European Union range from 1 to 6 per thousand inhabitants [
1]. Although this number is considerably lower when compared with the prevalence of cocaine, cannabis and other illicit drug use, dependence rates are much higher among opiate users [
2]. Opiates, heroin in particular, remain the primary drug for which individuals seek treatment and the vast majority of drug-related infectious diseases and mortality is associated with opiate use [
1]. Methadone substitution treatment is the standard, evidence-based treatment for opiate dependence in most countries [
3], but recently buprenorphine has been introduced as an alternative substitute drug to reduce heroin use and related health and social problems.
Given the chronic, relapsing nature of drug problems and the various life domains they affect [
4,
5], the attention for quality of life (QoL) in the field of drug abuse research has grown rapidly [
6]. The majority of these studies have assessed drug users’ health-related quality of life (HRQoL) [
7‐
9], especially among opiate-dependent individuals in treatment [
6]. Evidence is available that the HRQoL of opiate-dependent individuals is low in comparison with the general population and individuals suffering from other chronic diseases and most comparable with that of individuals with psychiatric problems [
10,
11]. In general, opiate-dependent individuals report poor mental health scores, while their scores for physical functioning are usually considerably higher [
12]. HRQoL is a concept frequently misused as a synonym for QoL [
13,
14]. It primarily focuses on the effects of a disease on individuals’ daily functioning [
15], with special attention for their physical and mental health [
11,
16].
The comprehensive concept of QoL has a more positive connotation and focuses on persons’ overall well-being and satisfaction with life [
17]. Such a holistic approach to QoL with attention for drug users’ own experiences and expectations is often lacking in drug abuse research. Up till now, the focus in most studies is exclusively on the absence of pathology and individuals’ functional status (HRQoL). However, it is necessary to make a distinction between HRQoL and QoL, since individuals’ health status may have an impact on QoL, but does not represent it [
18]. Health is included as an important domain in most QoL definitions [
13], but when individuals are asked to define important domains of QoL health is seldom mentioned as a primary domain [
19,
20]. A qualitative study concerning drug users’ perspectives on the concept QoL demonstrated that social inclusion and self-determination are regarded as central components of QoL [
20]. On the other hand, some quantitative studies have identified health-related issues as determinants of QoL [
21‐
23], illustrating the possible influence of health status on the concept QoL.
A limited number of studies have reported lower QoL scores for opiate-dependent individuals when compared with the general population or a non-clinical control group [
21,
24,
25]. Only recently QoL has become an outcome measure in research on the effectiveness of (various forms of) substitution treatment [
3,
26‐
28]. In general, opiate-dependent individuals report low QoL and HRQoL scores at admission to substitution treatment [
12]. Participation in substitution treatment brings about positive effects on individuals’ HRQoL and QoL, especially during the first months of treatment [
9,
28‐
33]. However, a stabilization of these improvements or even less favorable outcomes can be noticed from a long-term perspective [
30,
34].
A better understanding of determinants that are associated with high QoL scores may advice treatment services and policymakers how they can improve individuals’ QoL [
35]. Studies that provide information on predictors of QoL among opiate-dependent persons are limited and have mainly focused on HRQoL. Moreover, these studies have not resulted in unequivocal findings. An inverse relationship between age and HRQoL has been shown in various studies [
36‐
38], while inconsistent findings have been reported regarding the role of gender [
10,
30,
36,
38,
39]. The impact of severity of dependence on HRQoL remains unclear [
10,
36,
40‐
42], but the negative impact of excessive alcohol use on HRQoL has been demonstrated in several studies [
8,
41,
43]. Emotional and psychiatric problems (e.g., depression, personality disorders) appear to have a detrimental impact on individuals’ HRQoL [
36,
44,
45]. Social support may have a positive influence on HRQoL [
7], but conflicts with family and partner have been associated with lower HRQoL scores [
41]. As demonstrated by Millson and colleagues [
36], who identified more than a dozen different determinants of the mental and physical composite scores of the SF-36, opiate-dependent individuals’ HRQOL is affected by multiple factors.
Besides the limited number of studies on determinants of QoL, few authors have controlled for the influence of potential covariates in a multivariate design. Consequently, results are often limited to bivariate analyses of correlates of QoL [
25,
46,
47]. Despite the specific treatment needs of opiate users, only one study by Bizzarri and colleagues [
21] examined the independent impact of dual diagnosis, gender, age and current substance use on QoL of opiate-dependent individuals, using the WHOQOL-BREF. This study demonstrated a significant impact of dual diagnosis on all four QoL domains, a negative association of older age and female gender with some domains, while current substance use had no significant impact on QoL. Also, Conroy and colleagues [
48] found no association between QoL and drug-using practices (e.g., drug use, sharing of needle equipment) among injecting drug users, but a range of psychosocial factors (e.g., family support, having friends) influenced their current QoL. According to another study, the overall QoL of substance users in treatment was negatively associated with older age, specific medical conditions (i.e., arthritis, ulcers), severity of drug use, being treated in a detoxification unit and recent hospitalization for mental health problems [
22]. Finally, improvement of psychiatric symptoms was demonstrated to be the best predictor of increased QoL among severely mentally ill substance abusers [
23].
Given the dearth of research on predictors of QoL among opiate-dependent individuals and given the assumption that substitution treatment contributes to the stabilization of opiate users’ living situation, the aim of this article is to study the current QoL of persons who started outpatient methadone treatment at least 5 years ago. Furthermore, the influence of recent heroin use and psychological distress on current QoL is assessed, as well as the question which demographic, psychosocial, drug and health-related variables are independent predictors of a better QoL.
Discussion
This study revealed low QoL scores on various domains among opiate-dependent individuals 5–10 years after they had started outpatient methadone treatment. Although no general population norms are available with which these results can be compared, a significantly higher proportion of the study sample reported low QoL on six of the ten LQOLP domains in comparison with hospitalized male psychiatric patients [
58]. This finding can be partly explained by the high prevalence of psychological complaints in the study sample. Various studies have demonstrated high psychiatric co-morbidity in opiate-dependent individuals (in methadone treatment) [
45,
73‐
75]. Previous studies on QoL of opiate-dependent individuals have reported lower QoL scores among persons with co-occurring psychiatric problems when compared with individuals without psychiatric co-morbidity [
12]. Similar findings can be observed in studies among persons with severe mental illnesses, in which a negative effect of substance abuse on QoL has been demonstrated [
76,
77]. It appears that individuals with a so-called dual diagnosis are more vulnerable for having a poor QoL. Given the high prevalence of psychological symptoms in opiate-dependent individuals, it can be questioned whether it would not be more appropriate to develop integrated mental health and substance abuse services as the standard of care [
78].
Persons who started methadone treatment more than 5 years ago are generally dissatisfied with their “finances”. This has also been observed in other studies that have used the LQOLP to assess the effectiveness of opiate substitution treatment [
33,
34,
54‐
56]. The dissatisfaction with their financial situation may not be surprising, given the high cost of supporting a drug consumption habit [
79] and drug users’ substantial debts. Individuals’ poor education and unemployment may further affect their social and economic situation [
45,
80,
81]. Yet, the domain “finances” also appears to be the domain with the lowest satisfaction among the general population [
82].
The high mean score on the domain “framework” shows that opiate-dependent individuals have a sense of purpose with their life and future plans that give them satisfaction. Life meaning is important to buffer stress, and has in its turn a positive influence on QoL [
83]. Studies by Moomal [
84] and Zika and Chamberlain [
85] have demonstrated a clear association between life meaning and psychological well-being. Life meaning is a domain that needs more attention in QoL measurements, given the high importance that is attributed to this domain by persons with drug and mental health problems [
20,
53]. The high proportion of subjects who report a low QoL on the domain “fulfillment” indicates that many opiate-dependent individuals think it will be very difficult to actually realize their desired life goals. Experiences of stigma [
86] and discrimination [
87] often hinder drug users in their daily functioning and are associated with poor mental and physical health [
88].
Low scores on one QoL domain do not necessarily imply low scores on another domain, illustrating the necessity to assess QoL from a multidimensional perspective. The relatively high scores on the domain “health” demonstrate the appropriateness of methadone programs for reducing health problems, but—in combination with the previous observation—also stress the need for looking beyond health-related aspects. Generally, measuring QoL should be given a more prominent role in the assessment and monitoring of drug problems, starting from individuals’ needs and expectations in order to postulate and adjust treatment goals [
89].
To our knowledge, this is the first study applying a multivariate design to assess the independent impact of various demographic, psychosocial, drug- and health-related determinants on QoL among opiate-dependent individuals who started methadone treatment at least 5 years ago. This study confirms the findings of Conroy [
48] and Bizzarri [
21], who found no association between drug-related variables and the QoL of injecting drug users. Neither the ASI composite scores for drugs and alcohol, nor other drug-related variables, nor current treatment status were significant determinants of QoL. Also, in a validation study of the IDUQOL [
90], very low and non-significant correlations were observed between several drug-related variables and overall QoL. Bivariate comparisons of study subjects who recently used heroin and persons who did not do so, only showed a significantly lower mean QoL score for the domain “finances” among current heroin users. These findings illustrate the limited influence of severity of drug use problems on current QoL and highlight the need for treatment goals other than stopping or reducing drug use. Being abstinent from drugs or reduced drug problem severity is not necessarily accompanied by improvements in QoL, since giving up the positive aspects associated with drug use (e.g., prestige/status in the drug scene) and coping with various stressors (e.g., loneliness, boredom, discrimination) may have a negative impact on individuals’ QoL [
20].
Psychological distress appears to have the strongest negative impact on current QoL. As much as 25% of the variance of total QoL was independently explained by the severity of psychological distress. Also, taking medication for psychological complaints has a strong negative impact on QoL. Both determinants demonstrate the strong negative impact of psychological problems on the current QoL of opiate-dependent individuals. Consequently, early identification of psychological problems based on systematic assessment procedures and attention for the issue of co-morbidity during the treatment process is a prerequisite in methadone treatment.
Contextual factors, such as having a good friend and a structured daily activity, had a significant positive influence on the total QoL of opiate-dependent individuals. The protective role of social support on drug consumption [
91,
92] and retention in treatment [
93] has been shown in various studies. The observation that social networks have a positive impact on opiate-dependent persons’ QoL stresses the need for establishing individuals’ (non-professional) social networks during and after methadone treatment in order to enhance their social inclusion. This is further illustrated by the positive impact of having daily activities on total QoL: not necessarily employment, but having a meaningful plan for the day showed a positive association with total QoL
. Meaningful day activities and social support are both generic determinants of QoL and have also been identified as protective factors for QoL among the general population and specific subpopulations (e.g., persons with depressive disorders, disabilities) [
94‐
98]. The inability to change one’s living situation during the past year further had a significant negative impact on persons’ total QoL. The importance of stable housing for individuals’ QoL has been recognized in various studies on QoL of dually diagnosed individuals [
48,
99]. These independent correlates of QoL illustrate the need to assist opiate users in methadone treatment with housing and occupational issues. The influence of elements other than health-related factors (e.g., having an occupation, a good friend) on QoL cannot be underestimated. Due to a unilateral focus on health, caregivers may only have a partial picture of clients’ QoL and the various factors influencing it [
19]. Furthermore, improving one’s QoL [
17,
100] and tackling non-health-related problems (e.g., family relations, legal status, employment status) have been identified as the main reasons for going into treatment [
38].
Ultimately, this study has revealed that opiate-dependent individuals still need support on various life domains 5–10 years after starting methadone treatment and that a satisfactory QoL is in particular mediated by psychological well-being and some psychosocial variables. Consequently, a more holistic approach to methadone maintenance—and drug treatment in general—is recommended, which goes beyond pharmaceutical maintenance and medical care to include specific attention for psychological complaints and support in housing, occupational and social inclusion issues [
36,
45,
101].
Limitations of the study
Some limitations of this study should be taken into account. First, the sample size (
n = 159) was relatively small. Findings may therefore not be generalized to other groups of opiate users. Second, respondents were not selected randomly, nor did we apply a controlled design. It is unclear if the sample was fully representative for the group of opiate-dependent individuals starting methadone treatment 5–10 years ago (
n = 1,500), but the age and gender distribution of the sample was identical to that of persons in outpatient methadone treatment in the region of Ghent between 1997 and 2002 [
50]. The representativeness of the sample was enhanced by applying various strategies to recruit study participants (e.g., flyers, media campaign, contacts with drug, health and social services). It would further be interesting to focus in future research on the QoL of other groups of drug users (e.g., cocaine users, opiate users out of treatment) [
102] and compare these findings with those reported here. Third, given the cross-sectional design of the study, causality could not be examined. This study only reports associations, because possible determinants and outcomes were measured at the same time. Future longitudinal research should address issues of directionality and linearity. Fourth, psychological distress was measured by means of a short symptom checklist (BSI). Consequently, the prevalence of psychiatric disorders was not assessed, as no standardized diagnostic instrument was used. Still, validation studies have shown high correlations between BSI subscales and diagnostic instruments measuring the same constructs [
68]. Fifth, 60% of the variance of total QoL was explained by our final regression model, illustrating that other factors (not included in the model) will have had an impact on total QoL. Qualitative in-depth interviews could provide more information on how drug users perceive QoL and on factors that affect the QoL of drug-using individuals [
20,
103]. Finally, given the conceptual discrepancy between QoL and HRQoL, researchers need to make explicit what they are measuring exactly. Therefore, it would be interesting to compare both concepts—QoL and HRQoL—in future research, in order to illustrate the different conceptualization of both concepts.