Lancet. 1983 Dec; 2(8364): 1394-6.

Acupuncture relief of chronic pain syndrome correlates with increased plasma met-enkephalin concentrations.

Kiser RS, Khatami MJ, Gatchel RJ, Huang XY, Bhatia K, Altshuler KZ.

In twenty patients with chronic pain syndrome, acupuncture treatment resulted in significant improvement of both pain and psychiatric symptoms and higher plasma concentrations of metenkephalin. Plasma beta-endorphin concentrations were unchanged. The degree of symptom relief was correlated with the increase in plasma met-enkephalin.