Placebo is a beneficial effect produced by a placebo drug or treatment, which cannot be attributed to the properties of the placebo itself, and must therefore be due to the patient's belief in that treatment. This could be a real problem when interpreting the results of the diagnostic procedures but in cases of applying a therapy it could actually be quite helpful since it can enhance a chance of positive outcome. The incidence of placebo response is quite high and can approach 30-40% depending on circumstances.
Nocebo, the negative effect of the treatment related to patient's perception alone could be a real issue. It makes it difficult to deal with the treatment-avoiders: patients whose imagined side effects lead them to stop or refuse treatment. Patients experience imagined, or even real, adverse effects because they believe the treatment is causing them harm. Or, they belive, and frequently without a solid reason that the treatment will not help them or even harm them based on the remote experience of the friend or relative which may not even be related to the recommendations given to them. In general, human beings feel regret from the bad outcome resulted from the action taken rather than bad outcome that occurred from not taking action. As providers of health care remedies we are sometimes in a difficult position when there's a standard of care treatment, but our patients can't get past their fear of harm to try it. We understand and respect patient's decisions, we are happy to discuss things as many times as needed and understand that it may require additional visits to build enough trust to follow our recommendations.