double-blind
adjective [ usually before noun ]
ukus(also double-blinded)used to describe a test of a new product, especially a medicine, in which one group of people is given the new product, and another group is given something that contains none of the product. Neither those being tested nor those doing the testing know which group is which:
double-blind study/trial This is a double-blind trial of 400 patients where 60% will get the drug and 40% will get a placebo.