That highly publicized study about placebos being as effective as some antidepressants may have you wondering how this can be. The answer could surprise you.

First, what exactly is a placebo? Popularly called a "sugar pill" or "dummy pill," a placebo is a sham treatment. Placebos are often used in clinical drug trials to determine whether a new treatment is better than a lookalike but inactive pill.

These studies can produce peculiar findings. Sometimes volunteers are thrilled at the great results they're getting from this new wonder drug. And then afterward they may find out they were in the placebo group. What a letdown!

Yet how can something so fake produce such seemingly real results? Chalk it up mostly to human nature.

"Expectation is a powerful thing," says Dr. Robert DeLap of the U.S. Food and Drug Administration (FDA). "The more you believe you're going to benefit from a treatment, the more likely it is that you will experience a benefit."

The fact that many diseases have their flare-ups and remissions also contributes to this phenomenon.

Researchers have seen the placebo effect in conditions ranging from depression to arthritis to prostate enlargement. In fact, in many drug trials about one-third of the participants report improvement from a placebo, the FDA says.

Doctors are still trying to figure out how to harness the placebo effect. After all, it shows how powerful the mind can be over matter.