Pets in pain: countering the caregiver placebo effect

June 12th, 2014

Clinical trials involving pets are much more difficult to execute due to what is called the “caregiver placebo effect.” This is where the observations of the caregiver influence the true effect of the medical trial. In these types of trials, which are mostly performed to test pain medications, clinicians and scientists are once removed from the patient and the caregiver gives an assessment on how the treatment affects their pet. How the owner and the pet behave can actually influence the result of the trial.

To counter this placebo effect, researchers have carefully designed tools to distinguish the real effect of the medicine and the imagined effect. Two researchers, Margaret Gruen and Duncan Lascelles, performed tests using a low dose pain medication in cats with degenerative joint disease. The trial went as follows:

  • During the first two weeks, all participants were given a placebo to get them used to taking medication. The owners were aware they were giving the placebo.
  • In the following three weeks, half of the participants were given the real drug while the other half continued with the placebo. Neither group knew which group was taking which.
  • In the last three weeks, known as the “blinded placebo washout phase,” all the participants were given the placebo again but none of the owners knew about the change.

According to Gruen, the last 3 weeks were key in determining the usefulness of the drug. During the three weeks in which the medication was given, all of the participants stated that their pets' condition improved, and this was due to the placebo effect. But during the washout phase, the pet owners who had previously been given the real drug said their pets’ pains were returning, while the ones that received the placebo didn't notice any change.

By designing the trial in this way, the researchers were able to conclude that the drug was effective in cats with degenerative joint disease. According to Gruen, while this experiment could use further investigation, it is definitely useful in veterinary and human clinical trials to help counter the caregiver placebo effect.