Depending on the nature of the experiment, it's not that hard, e.g. http://www.gwern.net/Nootropics#adderall-blind-testing
:) I did almost type "impossible" instead of "very difficult". I'm one of those people who believes nothing is impossible, not even skiing through a revolving door (with short enough skis . . . ).
Depending on the nature of the experiment, it's not that hard, e.g. http://www.gwern.net/Nootropics#adderall-blind-testing