Nociceptive: pain from activation of nociceptors by actual or threatened tissue damage, with a normally functioning somatosensory system. Neuropathic: pain caused by a lesion or disease of the somatosensory nervous system. Nociplastic: pain arising from altered nociception without clear evidence of tissue damage or a somatosensory lesion (IASP, adopted 2017) — common in fibromyalgia, nonspecific chronic low back pain, and other central-sensitization states. "Mixed" describes overlap and is widely used clinically, though it isn't an official IASP category.

From the IASP/WHO classification of chronic pain for ICD‑11 (Treede et al., Pain, 2019). Chronic primary pain (MG30.0) applies when pain is the disease itself — e.g. fibromyalgia or nonspecific chronic low back pain — with significant distress or disability not better explained by another condition; the six secondary categories apply when pain is a symptom of an identifiable underlying disease. This is a reference classification for clinical reasoning — it doesn't replace the ICD‑10 code above.

Engel's biopsychosocial model — the consensus framework for chronic pain formulation, since outcomes are shaped by biological, psychological, and social factors together rather than by pathology alone.

Webster & Webster (2005). Best administered before starting opioid therapy; scores classify low (0–3, ~5.6% historical rate of aberrant behavior), moderate (4–7, ~28%), or high (≥8, ~91%) risk — a prompt for closer monitoring and structured agreements, not a reason to deny treatment on its own.