The overall goal of the ABILITY study is to help improve pain diagnostics and treatment by developing an implementable clinical computerised decision support system based on individual patient characteristics.

The investigators hypothesize that successful pain control with opioids can be predicted before treatment initiation with advanced data analyses of data originating from pre-treatment EEG, QST and pain-related catastrophic thinking.

The primary objective of this study is the identification of markers that can be used to individualize treatment recommendations, i.e. to reliably predict the response of pain to opioids.

Markers are selected among the most promising data and machine-learning methods are used for the prediction. This includes determining the associations between a battery of selected pre-treatment clinical predictive markers and the analgesic effect of opioid treatment in opioid naïve chronic pain patients, including indication and responder identification.

The key secondary objectives are as follows: to investigate pre-treatment clinical predictive markers as predictors of opioid treatment efficacy and effectiveness in terms of the following:

• Pain intensity and unpleasantness
• Use of rescue analgesics
• Physical functioning
• Global improvement and satisfaction with treatment

Inclusion Criteria:

• Pain duration ≥ 3 months.
• Minimum baseline pain intensity ≥ 4 on a 0-10 numerical rating scale (over the past week).
• Maximum baseline pain intensity < 9 on a 0-10 numerical rating scale (over the past week).
• Prescribed opioid treatment (ATC: N02)
• Anticipated to stay on prescribed opioid treatment throughout the study, i.e. >14 days.
• Anticipated to stay on any concomitant non-opioid treatment throughout the study, i.e. >14 days.
• Subject may be male or female, age >18 years old.
• Is willing and able to comply with study procedures as judged by the site investigator.
• Subject has voluntarily signed and dated the study-specific informed consent form, approved by an Independent Ethics Committee, after the nature of the study has been explained and the subject has had the opportunity to ask questions. The informed consent form must be signed before any study-specific procedures are performed.

Exclusion Criteria:

• Has a mental incapacity or language barriers precluding adequate understanding of study procedures.
• Is considered by the site investigator unsuitable to participate in the study for any other reason, for instance due to a significant serious underlying condition.
• Recently received opioids on a daily basis (within the last 10 weeks).
• Current alcohol or substance abuse, according to the site investigator's medical judgement.
• Is anticipated to undergo a painful procedure(s) (e.g. surgery) during the study, which can interfere with the experience of the chronic pain condition for which the subject is to receive opioids.

Subjects with an insufficiently treated chronic pain condition (with non-opioids ± adjuvants), and expected to benefit from the administration of opioids (as necessary) to obtain freedom from pain.