Because both a doctor's and a patient's belief in the value of a treatment can affect its outcome, most drug trials are usually double-blind, which means that not only the patients, but also the doctors, are unaware of who is receiving a placebo and who is receiving the real drug.Almost all double-blind studies show some benefit to the people taking a placebo, but in actual clinical practice, there is evidence that for some conditions, positive responses to placebo may be as high as 80 to 90 percent. The reason is that in a real treatment, the placebo effect is enhanced by the doctor's and the patient's expectations that the treatment will work.