A placebo is another strategy used in research to reduce error. A placebo is an inactive pill, liquid or powder that has no treatment properties. In a placebo study, half of the patients would receive medicine while the other half would receive placebo. You would not be able to tell the medicine from the placebo. The idea behind a placebo study is to see if the results seen are truly due to what is inside the pill and not due to the person's expectations of what should happen. Cancer patients will always be offered at least the usual treatment now accepted by doctors. They would never be tricked into being untreated if an option were available. A placebo would be used in a cancer treatment study only as an addition to the best-known care. You will always be told that a placebo is involved in a study. You will always be told what your chances are for getting the active medicine or the placebo.

For example, a placebo study may decide to look at whether adding a new pill to a patient's usual chemotherapy helps with their cancer. Early laboratory studies seem to say that this new pill should help, but no one knows for sure. So although this pill is certainly new and cutting-edge, the researchers do not know if it is better in treating cancer in people. Maybe the pill will do nothing and maybe it will make things worse. If they somehow already knew the pill would be better, they would not need to do the study. It would be unethical not to let everyone have the pill with the chemotherapy.

At the start of the study, all of the patients would be sorted into treatment groups by chance. Neither the doctor nor the patient would have any say which group the patient will be sorted into. The patients will not know which group they are in. Both groups would now start their treatment. Notice that both groups would receive the usual chemotherapy that doctors think is best. Both groups also swallowed pills, but only some of the patients received the active medicine inside the pill. This is fair because everyone had the same chance to be in either group. It is also fair because although only the people who had taken the active medicine will benefit if the pill is good, they alone will take on the risks if the pill makes their condition worse.