Background: Complementary and alternative medicine is a non-conventional therapy and includes a wide range of medical treatments in different countries. This study was done to evaluate alternative medicine complaints lodged to the Tehran Forensic Medicine Organization from 2011-2017.Methods: In this cross-sectional study, all documented complaints of complementary medicine lodged to the Tehran Forensic Medicine Organization from 2011-2017 were reviewed and assessed with retrospective follow-up. The inclusion criterion was complaints from complementary and alternative medicine, and the exclusion criterion was incomplete data. The study data included patients’ demographic data, the therapist, the specialty of the therapist, type of disease, treatment method, adverse effects, the initial and final decision by the commission, and the amount of medical error. This information was extracted from the existing documents and recoded in the checklists.Results: Medical errors were found in 53.4% of the complaints examined. The most common cause of complaint (63%) was the adverse effects, of which the most common ones were phytotherapy (45.2%) and cupping (Hijama) (20.5%). The error was significantly different between physician and non-physician healers (P=0.001).Conclusion: Based on this study, among the alternative medicine complaints lodged to the Tehran Forensic Medicine Organization from 2011-2017, the adverse effects were the main problem of complementary therapies confirmed in more than half of the complaints.