I was reading through Skeptic magazine and came upon an articel by Harriet Hall or the Skeptdoc. It was very good in explaining the placebo effect. I will summerize her main points here. First Placebo is latin for "I please". It is shown by the scientific method that people respond to placebos approximately 35% of the time. That is why in medical research into treatment is almost always compared to placebo. If the treatment is real, it must have an effect more than 35%. If there is no placebo in the control group then something may look like it does have an effect when it does not. This is a lot what alternative medicine studies by the those practitioners do. If you are told that something works and you believe it works it will. And there is hierarchy of effective placebos, and they are 1. placebo surgery, 2. placebo injections, 3. Sham acupuncture, 4. capsules 5. big pills, 6. more dose per day the better, 7. the more expensive the better, 8. the color of the pill makes a difference, and 9. telling the patient "This will relieve your pain," works better than "This might help." There are also nocebo, I harm, effects. People will report side effects from the placebo. That is also why in medical studies the side effects of a drug are compared to the side effects of the placebo, sorry nocebo. The effect is primarily subjective. They don't work on people who are unconscious or asleep. They don't do anything that can be measured objectively. They work for things like; headaches, itching, shortness of breath, tension, indigestion, depression and other symptoms that there are no objective measures for and we must rely on the patients self reporting. This doesn't imply that those effects are not real for the patient. Some say there is a objective changes, such as painting a wart with a dye that causes the wart to go away. Or was the wart going to go away on its own anyway? The mechanism of placebo effect relies on the following hypothesis; 1. expectancy, if you expect something to work, it usually will. This is a well known psychological effect. 2. Motivation, the need or desire for something to work. 3. Conditioning, the body learns physiological responses. Case in point is Pavlov dogs experiments in the early 2oth century. and 4. endogenous opiates are pain relieving chemicals that our own bodies make. Can animals have placebo effects. The believers in homeopathy and accupuncture say that animals cannot and that proves that the treatments work. Veterinary literature accepts the reality of placebos. Animals can develop learned physiologic response to a drun and then respond similiarly to a substituted placebo. Animals respond to attention and care from humans. Human owners can experience the placebo effect for their animals by perceiving a response when there really is none. And animals cannot talk so we have to interpret their behavior and this may or maynot be accurate. I will leave ethics to another time. The article by the Skeptdoc in Skeptics magazine was excellent and I recommend you read if you want to get the full dose.