Assessment of clinical, psychological, and psychophysical variables

(a) Opioid exposure Self-reported opioid use was considered the factor of interest assessed by a specific questionnaire that evaluated all medications used and their daily doses (e.g., antidepressants, anticonvulsant, hypnotic, analgesics non-opioid and opioid, etc.). Analgesic use was assessed by the self-reported average of analgesics used per week during the last three months. We defined opioid exposure using a categorical classification that combined information from pharmacy records of opioid medications dispensed and self-report information concerning recent opioid use. For data analysis, analgesic use was included as a dichotomous variable. We chose this strategy because subjects with chronic pain typically use rescue analgesics irregularly, and their frequency of use changes each day according to their pain level. Thereby, it would be difficult to quantify the precision of doses used to convert to morphine equivalent amounts and the exposure time. Thus, we used a simple based on the classification of opioid exposure or non-exposure in the last three months. The types of opioid medications used were classified according to classes [e.g., opium alkaloids (morphine, codeine), semisynthetic (oxycodone), or synthetic (methadone).

(b) The American College of Rheumatology (ACR)¹ Criteria were used in physician-administered and patient self-administered questionnaires, increasing the correct diagnoses. The scale of fibromyalgia symptoms ranging from 0 to 3 and adding the widespread pain index (WPI) to the modified severity scale (SS scale), when administered to patients with and without fibromyalgia, using a score ≥ 13 as the cut-off point for positive and negative diagnosis, enabled a 93.0% correct diagnosis, with 96.6% sensitivity and 91.8% specificity.

(c) Brazilian Profile of Chronic Pain: Screen (B-PCP: S) The B-PCP:S consists of four questions related to pain severity, six questions related to pain's interference with functioning, and five questions related to emotional burden²⁷. The pain intensity was assessed with a Numerical Pain Scale (NPS) score ranging from no pain (zero) to the worst possible pain (10). They were asked to answer the following question using the pain NPS: considering your pain, how intense was your worst pain during the most days at last 3 months.

(d) The Pittsburgh Sleep Quality Index (PSQI) The PSQI assesses sleep quality during the previous three months. It consists of 19 self-rated questions and five questions rated by the bed partner or roommate. These 19 items are grouped into seven component scores, each weighted equally on a 0–3 scale. The seven component scores are then summed to yield a global PSQI score, which has a range from 0 to 21; higher scores indicate worse sleep quality^28,29.

(e) The central sensitization inventory (CSI) This tool identifies key symptoms related to central sensitization processes by quantifying the degree of these symptoms. It consists of two parts: Part A is a 25-item self-report questionnaire designed to assess symptoms related to health and Part B (not rated) is designed to determine if one or more specific disorders³⁰.

(f) Sociodemographic Questionnaire Encompassed information related to age, years of study, body mass index (BMI), and questions related to clinical diagnoses, health problems (self-reported), and use of medication.

(g) Mini-International Neuropsychiatric Interview (MINI³¹) The MINI is a short (15–30 min) structured diagnostic interview aimed to screen for DSM-IV and ICD-10 diagnoses. In the present study, we reported information related to major depressive and maniac episodes, panic disorder, social phobia, obsessive–compulsive disorder, post-traumatic stress disorder, and generalized anxiety disorder.

(h) Quantitative Sensory Testing (QST) The QST with a computerized version of thermotest was used to determine the upper tolerance temperature and the heat pain threshold positioning the thermostat in the non-dominant ventral forearm. The temperature initiates at 32 °C and heated at a rate of 1.0 °C/s to a maximum of 52 °C. The participant reports the increase of the heat stimulus and presses the button when it was unable to tolerate it.