Do antidepressants work? Since the introduction of Prozac in the 1980s, prescriptions for antidepressants have soared 400 percent, with 17 million Americans currently taking some form of the drug. But how much good is the medication itself doing? "The difference between the effect of a placebo and the effect of an antidepressant is minimal for most people," says Harvard scientist Irving Kirsch. Will Kirsch's research, and the work of others, change the $11.3 billion antidepressant industry? Lesley Stahl investigates. The following script is from "Treating Depression" which aired on Feb. 19, 2012. Lesley Stahl is the correspondent. Richard Bonin, producer. The medical community is at war - battling over the scientific research and writings of a psychologist named Irving Kirsch. The fight is about antidepressants, and Kirsch's questioning of whether they work. Kirsch's views are of vital interest to the 17 million Americans who take the drugs, including children as young as six and to the pharmaceutical industry that brings in $11.3 billion a year selling them. Irving Kirsch is the associate director of the Placebo Studies Program at Harvard Medical School, and he says that his research challenges the very effectiveness of antidepressants. Irving Kirsch: The difference between the effect of a placebo and the effect of an antidepressant is minimal for most people. Lesley Stahl: So you're saying if they took a sugar pill, they'd have the same effect? Irving Kirsch: They'd have almost as large an effect and whatever difference there would be would be clinically insignificant. Stahl: But people are getting better taking antidepressants. I know them. Kirsch: Oh, yes. Stahl: We all know them. Kirsch: People get better when they take the drug. But it's not the chemical ingredients of the drug that are making them better. Irving Kirsch's specialty has been the study of the placebo effect: the taking of a dummy pill without any medication in it that creates an expectation of healing that is so powerful, symptoms are actually alleviated. Kirsch: This is the placebo response... Kirsch, who's been studying placebos for 36 years, says "sugar pills" can work miracles. Kirsch: Placebos are great for treating a number of disorders: irritable bowel syndrome, repetitive strain injuries, ulcers, Parkinson's disease. Even traumatic knee pain. In this clinical trial some patients with osteoarthritis underwent knee surgery. While others had their knees merely opened and then sewn right back up. Kirsch: And here's what happened. In terms of walking and climbing, the people who got the placebo actually did better-- Stahl: Come on.