What is a double-blind, placebo controlled study?

A double-blind, placebo controlled study follows a specific set of procedures to ensure that the results obtained are dependable and free from subjective bias. It is considered the 'gold standard' of clinical research studies. 

Until the study is complete, neither the study researchers nor the participants know who received the study test substance, and who received an identical dummy substance, called a placebo. This 'blindness' ensures that the personal beliefs and expectations of either the researchers or the study subjects do not undermine the objectivity of the results.