The results of this systematic review confirmed the hypotheses of this review.

There is not sufficient evidence to support or refute the existence of OIH in humans except in the case of normal volunteers receiving opioid infusions. Prospective CPP clinical studies measuring ptrs and tolerances pre- and post-opioid placement with CPP non-opioid control groups are required.

There is consistent evidence by all methods that NP is present in CLBP and STS. Reported prevalence percentages by all methods are substantial. This has significant implications for the treatment of CLBP and STS.

These studies solidify the evidence for an association between pain and SI, SA, and SC in both CPPs and other than APPs/CPPs.

Somatization is commonly associated with chronic pain and may relate to pain levels.