Placebo patients know that they have received a treatment, so that introduces a bias in the reporting of outcomes from the patient, even if the medics are blinded. If you believe you have been treated it is well known that patients report improvements even for illnesses that can be measured not to have improved.
The breaking of blinding and contrary measurements is enough to undermine most claims for placebo.
The breaking of blinding and contrary measurements is enough to undermine most claims for placebo.