A placebo has been defined as "a substance or procedure ... that is objectively without specific activity for the condition being treated". Under this definition, a wide variety of things can be placebos and exhibit a placebo effect. Pharmacological substances administered through any means can act as placebos, including pills, creams, inhalants, and injections. Medical devices such as ultrasound can act as placebos. Sham surgery, sham electrodes implanted in the brain, and sham acupuncture, either with sham needles or on fake acupuncture points, have all exhibited placebo effects. Bedding not treated to reduce allergies has been used as a placebo to control for treated bedding. The physician has even been called a placebo. A study found that patient recovery can be increased by words that suggest the patient “would be better in a few days”, and if the patient is given treatment, that “the treatment would certainly make him better” rather than negative words such as “"I am not sure that the treatment I am going to give you will have an effect". The placebo effect may be a component of pharmacological therapies: Pain killing and anxiety reducing drugs that are infused secretly without an individual’s knowledge are less effective (in the latter case no more so than saline) than when a patient knows they are receiving them. Likewise, the effects of stimulation from implanted electrodes in the brains of those with advanced Parkinson’s disease are greater when they are aware they are receiving this stimulation.
The placebo effect has sometimes been defined as a physiological effect caused by the placebo, but Moerman and Jonas have pointed out that this seems illogical, as a placebo is an inert substance which does not directly cause anything. Instead they introduced the word "meaning response" for the meaning the brain associates with the placebo, which causes a physiological placebo effect. They propose that the placebo, which may be unethical, could be avoided entirely if doctors comfort and encourage their patients' health. Ernst and Resch also attempted to distinguish between the "true" and "perceived" placebo effect, as they argued that some of the effects attributed to the placebo effect could be due to other factors.
The placebo effect has been controversial throughout history. Notable medical organizations
have endorsed it, but in 1903 Richard Cabot concluded that it should be avoided because
it is deceptive. Newman points out the "placebo paradox", -