"The benefits, risks, burdens, and effectiveness of the new methods should be tested against those of the best current prophylactic, diagnostic, and therapeutic methods. This does not exclude the use of placebo or no treatment in studies where no proven prophylactic, or therapeutic methods exist." World Medical Association (WMA) Declaration of Helsinki.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2647647/ for more.