Clinical epidemiology of substance use disorders: Understanding patterns, sharing knowledge, planning interventions

Substance use disorders (SUDs) make a large contribution to the burden of diseases, and the information gathered from affected individuals is often insufficient to inform adequate interventions1. The implementation and expansion of epidemiological surveys can fill data gaps and offer the opportunity to understand the progression of the disease, share global strategies and identify the best local solutions. Due to the concerted efforts of health professionals and patients to alleviate the consequences of the disease, the observation of the natural course of SUDs has been changing into the evaluation of its course in response to treatment following evidence-based approaches. Thus, clinical epidemiology has extended from the estimation of incidence and prevalence of diseases in a population, to include the long-term follow up of patients and anticipate the full development of data-based epidemiology of prevention.

The study by Chavan et al2 in this issue is the first comprehensive SUD report of Punjab, India and is part of the National Mental Health Survey. Using a reliable sampling method and standardized procedures, the researchers found a prevalence of alcohol and other SUDs higher than 10 per cent in the region. In particular, more than one of three households in Punjab had at least one person with SUD, alcohol was the most commonly used substance, tobacco had a culturally bound limited use and opioids were predominant among persons with illicit drug use. Future surveys and a longitudinal observation will help define disease patterns and monitor the validity of the interventions. Interestingly, the authors have identified and highlighted the existence of an 80 per cent treatment gap for the local SUD population. Globally, about one in six people who suffer from SUDs receive treatment each year, and the accessibility and availability of services for such conditions are limited3. The gap is wide if we compare one in 18 who receive treatment in Africa with one in five who are treated in the US and Europe. This points to large disparities between regions while confirming overall the inadequacy of the response3. Without overlooking significant socio-cultural differences, there is a global need to improve disease education, enhance prevention and promote awareness and treatment readiness while reducing the stigma. However, this would be insufficient if we do not step up our efforts to identify and abate treatment barriers.

A paradigmatic example is represented by the current opioid epidemic, a major public health threat accounting for 76 per cent of SUD-related deaths worldwide4. No policy is likely to substantially reduce these numbers in the short term, but predictive models suggest that adding medication and psychosocial support to overdose prevention and prescription control can bring about earlier results5. Thus, priority must be given to measures that reduce cost and increase long-term availability and accessibility of treatment to larger proportions of individuals with substance use problems than previously considered. This includes drug users who are not in severe conditions but still require interventions to prevent an escalation in their disability and comorbidity related to drug use.

About 12 million people have reported non-medical and illicit opioid use (problem use) in the US, based on the National Survey on Drug Use and Health6. This equals 3-4 times the amount of those who are more severely affected and have been the target of treatment. More concerning, the numbers of problem users have doubled in four years7, suggesting that this group is a main reservoir of a developing opioid use disorder (OUD). People with a few clinical symptoms are difficult to identify and do not usually seek help although they are at risk of developing a disease. Problem opioid users are no different, and those among them who have difficulty in complying with opioid therapy for pain can often be encountered in routine medical care. Close monitoring and coaching of these patients should be offered at the doctor's office and in stepwise fashion, with the option to deliver opioid antagonist or agonist substitution therapy as appropriate to those ones at risk of transitioning from a mild to a moderate use disorder. The feasibility and benefits of early interventions during the development of the disease have to be scientifically confirmed and could provide a new and effective preventive approach to SUDs.

Effective medications are gradually becoming more familiar to and 'user-ready' for primary care physicians, general practitioners and other healthcare professionals previously marginal to SUDs care. This has implied a public health and clinical discussion to change old policies and recommendations for treatment that were tailored to speciality clinics. In particular, the use and implementation of medication-assisted treatment (MAT) for OUD is now challenging some existing procedures. There are indications that buprenorphine and methadone treatments can be safely and efficiently delivered outside strict guidelines or the limitations imposed by highly regulated programmes8 while improving the quality of monitoring through the participation of multiple healthcare professional and the shared use of electronic health records and controlled substances reporting systems. The use of and compliance with opioid antagonist medications are being promoted by the adoption of long-acting naltrexone formulations and by improving treatment initiation outside the cautionary limits of inpatient detoxification and prolonged preliminary abstinence9.

The benefits of creating a large network of healthcare professionals who are willing to be more closely involved with OUD care, such as pharmacists, nurse practitioners and physician assistants, and offering access to multiple points of treatment for OUD to the patients can be significant and potentially long reaching. In addition to extended services, easy accessible community settings and improved treatment monitoring, a relative reduction in MAT prescribers' workload allows them to take new patients in treatment. More broadly, a significant increase in the capacity of other professionals to deliver treatment sets the stage to expand access to interventions for a wider range of SUDs. In sum, the growing awareness of the importance of a patient-centred approach argues for better-individualized care and for the overhaul of redundant practices that create barriers to treatment access and continued care.

The study of the epidemiology of SUDs is commonly included in mental health surveys. The investigation by Chavan et al2 found that 13 per cent of the SUDs population had other psychiatric problems, depression being the prevalent one by far (5.7%). Co-morbid SUDs are the most common psychiatric conditions associated with mental disorders and are present in larger amount in patients who receive protracted treatment and are more thoroughly evaluated and closely observed. The pooled prevalence of co-morbid SUDs and affective disorders can top 50 per cent in methadone-treated patients10. More research is needed on the diagnosis, progression and treatment of mental disorders among patients with SUDs and to determine the nature and entity of their influence on the outcome of substance use treatment. Further, given the urgent need to improve utilization of evidence-based pharmacotherapy for OUD to reduce morbidity and mortality11, the evaluation of medication interaction and adverse effects requires a thorough study to produce widely available guidelines for dual diagnosis populations. Methadone and buprenorphine have major interactions with commonly prescribed psychotropic medication, including increased risk of sedation, confusion and decreased respiratory rate. The cardiac effects, such as QT prolongation on electrocardiogram, and serotonergic stimulation are other synergic and potentially lethal risks12.

The relationship between mental health and SUDs is likely bidirectional and their co-occurrence is associated with a number of negative consequences, including relapse, hospitalizations, overdoses and suicide13. These complications are now on the rise and, needless to say, highlight the importance of studying the best way to manage such co-morbid conditions. The treatment of concurrent SUDs and chronic medical diseases has not been the focus of attention besides the role played by chronic pain, but it is probably as important in terms of quality of life and long-term outcomes of the patients14. Conditions such as diabetes and cardiovascular diseases require regular administration of life-saving medications and their presentation and full compliance with therapy are negatively affected by SUDs15. These diseases in turn may influence SUDs expression, course and prognosis. The identification of severely affected high-risk populations is another task unique to epidemiological studies, and it is a call for more effective interventions16.

In conclusion, the ubiquity and high prevalence of SUDs along with their co-morbid conditions make prevention, evaluation and treatment, a priority of the routine clinical practice in primary care that constitutes the gateway to health care management. The clinical epidemiology of SUDs is the foundation for understanding the intertwining of developmental, genetic and environmental correlates and may help clinicians to better tailor treatments to individual patients. In this sense, the longitudinal use of epidemiological surveys offers an increasingly sensible observational tool to verify the efficacy of treatments, make corrections where needed and identify areas in need of improvement. On this base, more effective primary prevention programmes can be developed with specific targets and measurable outcomes.