Placebo controls are necessary because many patients improve just by suggestion. The placebo effect refers to the improvement seen in patients on placebo. It can be enormously reassuring just to see a doctor and receive pills, even if there is no active ingredient in the pills. The placebo effect is a real phenomenon and can reach 30 to 40 percent in some treatment studies. Therefore, it is necessary to include a placebo control in a treatment study in order to prove that patient improvement is due to the active ingredient in the drug and not just to the placebo effect.