Terminology and prevalence
The lack of clarity regarding the risks of addiction to patients taking opioids in part relates to lack of consensus and interchangeability regarding the terms misuse, abuse, problematic use, dependence and addiction (see below for formal definitions). The term dependence has been argued to be a less stigmatising term than addiction. There has been traditionally a tendency to use the work dependence for a medication that causes withdrawal symptoms when stopped and to use the word addiction for the reliance on illicit substances and the lifestyle that accompanies this. The terms addiction and dependence are however used inconsistently and sometimes interchangeably by clinicians and potential service users. The problems seen in patients taking opioids for pain vary considerably from difficulty in reducing opioid dose because of withdrawal effects or re-emergence of pain to much more complex presentations characterised by many of the more difficult behaviours and complex psychosocial of continued opioid use. The heterogeneity of presentations can lead to difficulties for patients in accessing appropriate services to support opioid reduction. Primary care practitioners and pain specialists may lack expertise in identifying and managing patients with opioid dependence syndrome and treatment in addiction services may fail to meet the needs of a patient with pain who is (or who perceives themselves to be) deriving symptom relief from drugs which are otherwise problematic.
The best current evidence of addiction risk from samples treated for chronic pain in primary and specialty care estimates that 8-12% of long-term prescribed opioid users meet criteria for a current or past opioid use disorder. Published data do not allow firm conclusions to be drawn regarding the prevalence of addiction in the UK in people given opioids for the treatment of pain. Data from randomised clinical trials are unhelpful as trial duration is usually less than 12 weeks. Data from longer-term, open-label extensions of clinical trials are of limited use as there is little agreement on definitions in relation to problematic drug use (see below) and how this might be measured. In addition, study populations are not representative of the general population for whom opioids are prescribed as patients with mental health diagnoses and substance misuse disorders are usually excluded from clinical trials. Population-based studies may be more representative and tend to report greater prevalence of problematic use in those prescribed opioids in the longer term.
The literature is clear that patients with co-morbid mental health disorders, including past or current substance misuse disorders, are more likely to receive opioid prescriptions for pain, are more likely to use problematic high doses and are more likely to be co-prescribed other psychotropically active and centrally-acting medicines including benzodiazepines. This phenomenon has been described as ‘adverse selection’.
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