A large systematic review by researchers in the US, China and the University of Oxford, shows acupuncture should be given for at least five weeks in order to achieve 80% of maximum analgesic effect. A total of 77 randomised trials of acupuncture for chronic pain of the shoulder, neck, knee and lower back were included. They covered 8830 patients. Higher initial pain intensities were found to result in higher acupuncture pain relief.
(The response-time relationship and covariate effects of acupuncture for chronic pain: A systematic review and model-based longitudinal meta-analysis.European Journal of Pain, 13 June 2020.)