Non-Adherence to Pharmacotherapy: A Prospective Multicentre Study About Its Incidence and Its Causes Perceived by Chronic Pain Patients.

Objective: Pharmacological interventions remain the cornerstone of chronic pain treatment; however, nearly 40% of the prescription medicines are not taken as prescribed. The present study aims at understanding and describing non-adherence from the perspective of chronic pain patients during a 1-year follow-up study.

Methods: A cohort of 950 consecutive patients referred to a first consultation in Multidisciplinary Chronic Pain Clinics was followed with a standardized protocol for 1 year. This included assessment of pain characteristics; prescribed medication; therapeutic adherence; effectiveness of treatment, non-adherence and its perceived reasons; clinical outcomes and quality of life. We used a mixed methods approach, including qualitative and quantitative analyses.

Results: Forty-nine percent of the 562 patients who responded to all assessments during follow-up were adherent after 1 year of chronic pain treatment. The core associations between each "non-adherence reason" and Anatomical Therapeutic Chemical Code (ATC) group were perceived side effects (=0.019) and delayed start (=0.022) for narcotic analgesics (opioids); perceived non-efficacy (=0.017) and delayed start (=0.004) for antiepileptics and anticonvulsants; perceived low necessity (=0.041) and delayed start (=0.036) for analgesics antipyretics; change in prescriptions because of a new clinical condition for antidepressants (=0.024); high concerns (=0.045) and change in prescriptions because of a new clinical condition (<0.001) for non-steroidal anti-inflammatory drugs; delayed start (=0.016) and financial constraints (=0.018) for other medications.

Discussion: This study emphasizes the patient's perspective regarding non-adherence to pharmacological treatment of chronic pain, providing valuable and novel information to be used in future interventions to help patients make an informed choice about their adherence behavior.