40 pain-free volunteers took part in an experiment funded by the Arthritis Research Campaign using an artificial pain stimulus, and were led to expect reduced pain after the application of a cream which was actually a placebo.
Lead researcher Alison Watson said: "Any medical treatment involves a placebo element; the psychological suggestion that it is going to work. So we theorised that a proportion of any treatment's effectiveness would relate to how much we wanted it to work, believed in it or trusted the person administering it.
"Doctors and nurses can transmit a lot of information about a treatment and its effectiveness through their words and gestures. We know that when people visit their preferred GP the treatment or advice they receive will be more effective than that given by a GP they prefer not to see. Similarly, red pills have been shown to be more effective than green ones; so we wanted to test whether all this was due to expectations of successful treatment and trust in the person giving it."
24 of the volunteers initially received a moderately painful heat stimulus to both arms. The placebo cream was then applied to the skin, but they were led to believe that the cream on one of their arms may be a local anaesthetic.
After the application of the cream, the intensity of the heat stimulus was turned down on one arm without informing the volunteer. Subsequently the intensity was returned to its previous level, but - in contrast to the 16 people in the control group - 67% of the treatment group continued to perceive the heat as less painful.