In addition, dose-response effects have also been documented where two placebo pills were demonstrated to have more pronounced effects than one. The physiology of the placebo effect is still largely unknown. A placebo is chemically inactive, yet it has a profound effect on the human mind and body. A possible explanation is that a patient's belief in the treatment will reduce anxiety by allowing the problem to seem more controllable. With regards to the example given at the beginning of the paper, you may feel much more at ease once a doctor has told you that there are effective treatments for your pain, therefore you can reap the benefits of a less-stressed state.
Stress adversely affects several physiological processes and increases symptom reporting.
Thus, the patient may benefit from the relief of symptoms of depression, stress, and anxiety. Another explanation is the idea of conditioned stimuli. Thus, inactive drugs, people, procedures, and places can function as conditioned stimuli for the alleviation of symptoms if powerful unconditioned stimuli has been positively associated repeatedly with the relief of symptoms. Pain sensation is subject to circuitry within the nervous system that uses opioid synapses, as suggested by the fact that injection of opiates relieves pain. It is thought that possibly the placebo effect is a stimulation and release of our body's own natural narcotics, such as endorphins and enkephalins.