What is double blind drug trial?

A double-blind study means that neither the test subject (human) or the researcher administering the study knows whether the test subject is receiving the experimental treatment or the control treatment.

Often in human drug tests, the control treatment will be a placebo.

This ensures that neither party can make any expectations as to whether they should or shouldn't be seeing results. This is important because sometimes researchers will botch their results to coincide with their hypothesis. This also ensures that both control and experimental groups experience the "placebo effect" more or less equally