In studies about new medicines, researchers usually give one group of patients the medicine that is designed to treat an illness. They give another group of patients a placebo, which is taken the same way as the medicine but does not actually contain the ingredients of any medicine. Different medicines are tested in different experiments, but the placebos usually contain the same non-medical ingredients. If both groups of patients are healed, then researchers cannot be sure whether the medicine caused improvement, but if the group given the medicine is healed while the group given the placebo remains ill, researchers can conclude that the medicine causes the illness to go away.