BackgroundConditioned pain modulation (CPM) is impaired in people with chronic pain such as knee osteoarthritis (KOA). The purpose of this randomized, controlled clinical trial was to investigate whether strong electroacupuncture (EA) was more effective on chronic pain by strengthening the CPM function than weak EA or sham EA in patients with KOA.MethodsIn this multicenter, three-arm parallel, single-blind randomized controlled trial, 301 patients with KOA were randomly assigned. Patients were randomized into three groups based on EA current intensity: strong EA (>2mA), weak EA (<0.5mA), and sham EA (non-acupoint). Treatments consisted of five sessions per week, for 2weeks. Primary outcome measures were visual analog scale (VAS), CPM function, and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).ResultsThree hundred one patients with KOA were randomly assigned, among which 271 (90.0%) completed the study (mean age 63.93years old). One week of EA had a clinically important improvement in VAS and WOMAC but not in CPM function. After 2weeks treatment, EA improved VAS, CPM, and WOMAC compared with baseline. Compared with sham EA, weak EA (3.8; 95% CI 3.45, 4.15; P<.01) and strong EA (13.54; 95% CI 13.23, 13.85; P<.01) were better in improving CPM function. Compared with weak EA, strong EA was better in enhancing CPM function (9.73; 95% CI 9.44, 10.02; P<.01), as well as in reducing VAS and total WOMAC score.ConclusionEA should be administered for at least 2weeks to exert a clinically important effect on improving CPM function of KOA patients. Strong EA is better than weak or sham EA in alleviating pain intensity and inhibiting chronic pain.Trial registrationThis study was registered with the Chinese Clinical Trial Registry (ChiCTR-ICR-14005411), registered on 31 October 2014.