Every aspect of the body is controlled from the mind and the mind has levels of consciousness. The conscious aspects of the body are controlled by the conscious mind, and the unconscious aspects of the body are controlled by the unconscious mind. For instance, moving our arms or legs is conscious. We make the decision to move and the arm or leg moves accordingly. On the other hand, for most people, no amount of concentration will raise or lower blood pressure, increase serotonin levels in the brain or prevent an auto-immune disease from attacking the body’s own cells.
Just about any drug that a doctor will give you changes the way the body works. It may cause the body to produce more or less of a hormone or neurotransmitter, or block the effects of certain hormones or other compounds such as histamine, or change the actions of nerves and block pain etc. In other words, they change what the body already does, presumably because the way it is doing what it’s doing is not producing the desired outcomes.
These functions of the body are controlled from unconscious aspects of the mind. Hypnosis works on these aspects of the mind as do placebos.