The magnitude of the response varies with many factors, including the Expressed confidence of the clinician ("this is going to make you feel a lot better" vs "there is a chance this might help") Certainty of the patient's beliefs (effect is larger when patients are sure they are receiving an active drug than when they know there is a chance they are getting a placebo) Type of placebo (eg, injectable drugs have a larger placebo effect than oral ones) Not everyone responds to placebos, and it is not possible to predict who will respond; correlations between personality characteristics and response to placebos have been theorized but not well established.