Here is a link to a new meta-analysis, published in The Journal of Bone & Joint Surgery, this paper draws some parallels with what I have seen published in the past. Namely that patients have a complex physiological response to acupuncture that INCLUDES but is not LIMITED to placebo.
From the discussion:
“This meta-analysis demonstrates that acupuncture can result in both short and long-term improvement in function in patients with chronic knee pain due to osteoarthritis, but that the effect of pain relief is not sustained in the long term. Acupuncture tends to have better outcomes than sham acupuncture, usual care, and no intervention. These favorable effects of acupuncture involve complex interactions with the patient, including empathy, intention, care, and attention, that cannot be achieved by medications alone or by no intervention. In addition, endogenous chemicals released during the acupuncture process, such as enkephalin, dynorphin, and gamma-aminobutyric acid, may have distinct effects for patients with chronic knee pain.”
Lin, X., Huang, K., Zhu, G., Huang, Z., Qin, A., & Fan, S. (2016). The Effects of Acupuncture on Chronic Knee Pain Due to Osteoarthritis: A Meta-Analysis. The Journal of Bone & Joint Surgery.