Through the content analysis of information on placebo given to study participants, extracted data of 70 placebo control groups from 65 PILs were categorized into three groups. More than half of the PILs (57.1%) were straightforward to the participants when they were introducing placebo acupuncture control, and these were classified as FD group. In the 2nd group named as DD group, no words or phrases that clearly indicated placebo acupuncture would be used (35.7%), i.e., rather deceptive words such as ‘different (7),’ ‘control (5),’ ‘group 1 or group 2 (2),’ ‘non-traditional (2),’ ‘not typical (2),’ and ‘test (2),’ were given. Remaining five PILs (7.1%) fell into MI group and they missed out on explaining anything about a placebo control group. Detailed results of the content analysis are provided in Additional file 1: Appendix 4.