Dan Ariely puts drug reps under the microscope:
One clever tactic they used was to hire physicians to give a brief lecture to other physicians about a drug. Now, they really didn’t care what the audience took from the lecture, but were actually interested in what the act of giving the lecture did to the speaker himself. They found that after giving a short lecture about the benefits of a drug, the speaker would begin to believe his own words and soon prescribe accordingly. Psychological studies show that people quickly start believing whatever comes out of their own mouths, even when they are paid to say it. This is a clear case of cognitive dissonance at play; doctors reason that if they are touting this drug, they must believe in it themselves — and so their beliefs alter to align with their speech.