Fig 1.

(Used with permission from fig. 27.1, p. 363, Wall and Melzack's Textbook of Pain, 6th Edn., 2013, ISBN: 9780702040597). At the time of enrolment (the clinical corollary of which is the new patient assessment), pain severity is at its highest. Over time, even with no treatment, pain levels may reduce (natural history and perhaps regression to the mean). With treatment (drug or any treatment), the pain reduces to a greater degree, in part because of the ‘intrinsic’ treatment effect, and partly from the placebo effect.