Opioids have proven very useful for treatment of acute pain and cancer pain, and in the developed countries opioids are increasingly used for treatment of chronic non-malignant pain patients as well. This literature review aims at giving an overview of definitions, mechanisms, diagnostic criteria, incidence and prevalence of addiction in opioid treated pain patients, screening tools for assessing opioid addiction in chronic pain patients and recommendations regarding addiction problems in national and international guidelines for opioid treatment in cancer patients and chronic non-malignant pain patients. The review indicates that the prevalence of addiction varied from 0% up to 50% in chronic non-malignant pain patients, and from 0% to 7.7% in cancer patients depending of the subpopulation studied and the criteria used. The risk of addiction has to be considered when initiating long-term opioid treatment as addiction may result in poor pain control. Several screening tools were identified, but only a few were thoroughly validated with respect to validity and reliability. Most of the identified guidelines mention addiction as a potential problem. The guidelines in cancer pain management are concerned with the fact that pain may be under treated because of fear of addiction, and the guidelines in management of non-malignant pain patients include warnings of addiction. According to the literature, it seems appropriate and necessary to be aware of the problems associated with addiction during long-term opioid treatment, and specialised treatment facilities for pain management or addiction medicine should be consulted in these cases.

This study aimed to investigate the risk of death, development of cancer, and hospital inpatient admissions resulting from injuries and toxicity/poisoning among opioid users with chronic noncancer pain. A population-based cohort of 13,127 adults, who have participated in the Danish Health Interview Surveys in 2000 or 2005 and have been followed up prospectively by registers until the end of 2011, were classified according to the absence or presence of chronic pain (ie, pain lasting ⩾ 6 months) and long-term or short-term opioid use (individuals using at least 1 prescription per month for 6 months in the previous year and at least 1 prescription in the previous year, respectively). The risk of all-cause mortality was 1.72 (95% confidence interval [CI]=1.23-2.41) times higher among long-term opioid users than among individuals without chronic pain. The risk of death was lower, but still significantly higher in short-term (1.36, 95% CI=1.07-1.72) and non-opioid users with chronic pain (1.39, 95% CI=1.22-1.59) than in the background population. There was no statistically significant association between long-term opioid use and cardiovascular and cancer mortality. No deaths among opioid users were caused by accidents or suicides, although opioid users had higher risks of injuries and toxicity/poisoning resulting in hospital inpatient admissions than individuals without chronic pain. The risk of all-cause mortality was significantly higher among long-term opioid users, but no obvious associations between long-term opioid use and cause-specific mortality were observed. However, opioid use increased the risk of injuries and toxicity/poisoning resulting in hospital inpatient admissions.

Chronic pain is currently considered a public health problem with high costs to the individual and society. To improve prevention and treatment of chronic pain, epidemiologic studies are mandatory for assessing chronic pain. The aims of this study were to estimate the prevalence of chronic pain in the adult Danish population and to analyze associated factors such as diseases, immigration, and opioid use. This cross-sectional survey combines individual-based information from the Danish Health Survey (2010) and official Danish health and socioeconomic, individual-based registers. The simple random sample consisted of 25,000 individuals (≥16 years old) living in Denmark. In all, 60.7% completed a mailed or online questionnaire. Associations were examined with multiple logistic regression analysis. The study population consisted of 14,925 individuals in whom a high prevalence of chronic pain (26.8%, 95% confidence interval: 26.1 to 27.5) and a high prevalence of opioid consumption (4.5%) were observed. Other aspects of particular note: (1) a higher prevalence of chronic pain occurred among individuals with cardiovascular and chronic pulmonary diseases than among individuals with cancer; and (2) individuals with a non-Western background reported a higher pain prevalence, higher pain intensities, and more widespread pain than individuals with Danish background; however, opioids were more frequently used by native Danes. The prevalence of chronic pain as well as opioid use in Denmark are alarmingly high, and the relevance of opioid consumption is unknown.

We recommend that future research on opioid treatment does not only focus on biological issues. The effect of opioids needs to be viewed in a much more complex context where consequences like health related quality of life, depression and the role of various coping strategies are included.