Study design: this trial is a multi-central randomized controlled trial which contains 14 centers. Random sequences will be generated by the clinical evaluating center of China Academy of Chinese Medical Sciences. Subjects are patients who have severe chronic constipation.
Sample size evaluation: Sample size will be based on the proportion of patients having mean complete spontaneous bowel movements (CSBMs) no less than 3 times per week. The proportion is 31.67% in our phase I clinical trial by using electro-acupuncture, and 30.9% in another trial by using prucalopride.The total sample size is 560.
Periods and primary outcome: participants will be assessed at baseline for 2 weeks, treated for 8 weeks, and followed up for 24 weeks. Primary outcome is the proportion of patients having mean CSBMs/week no less than 3 times over the latter 6-week treatment.
Quality control: the study is a randomized controlled trial; participants were included strictly; evaluators and statisticians are blinded; quality control officers of 3 different levels will supervise this trial.
Data management: this trial will use the Remote Dara Capture (RDC) system for data entering and Data Verification Plan (DVP) for data examining.
Statistical analysis: Intention-To-Treat (ITT) analysis will be used in this study. One-sided test (non-inferiority) will be used for testing the primary outcomes; meanwhile, two-sided test will be used for evaluating other outcomes. A P value equal to or less than 0.05 is considered to indicate statistical significance.