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The placebo effect and animals

Researcher XJ wondered if the placebo effect occurs in primates or other animals. The placebo effect is a therapeutic effect (or generally positive effect) seen when a non-therapeutic treatment is administered. This is an interesting question. Wondering how to test it, XJ thought to see if a placebo effect is seen with addiction. That is, if a drug is given to animals and addiction occurs what happens if a fake drug is given instead? Would the fake drug induce highs? XJ also wondered about whether drug addiction and the placebo effect are mechanistically linked.

Given the questions asked several searches were done and resources collected. Pubmed, Google, ETBLAST and Faculty of 1000 were used to conduct the searches. Relevant results were not immediately obvious as clinical trials and experiments are done with the word placebo in the abstract and title. However, searching through the search hits resulted in references and discussions which asked whether animals do experience a placebo effect.

The search results are divided in the following four categories; a summary is provided after the reference list. The references provided are a good place to start a more detailed literature review.

  1. General information on the placebo effect
  2. References from the published literature on the placebo effect in animals
    1. Cracknell, Nina R, and Daniel S Mills. “A double-blind placebo-controlled study into the efficacy of a homeopathic remedy for fear of firework noises in the dog (Canis familiaris).” Veterinary Journal (London, England: 1997) 177, no. 1 (July 2008): 80-88.
    2. Drago, F, A Nicolosi, V Micale, and G Lo Menzo. “Placebo affects the performance of rats in models of depression: is it a good control for behavioral experiments?.” European Neuropsychopharmacology: The Journal of the European College of Neuropsychopharmacology 11, no. 3 (June 2001): 209-213.
    3. Jaeger, G T, S Larsen, and L Moe. “Stratification, blinding and placebo effect in a randomized, double blind placebo-controlled clinical trial of gold bead implantation in dogs with hip dysplasia.” Acta Veterinaria Scandinavica 46, no. 1-2 (2005): 57-68.
    4. McMillan, F D. “The placebo effect in animals.” Journal of the American Veterinary Medical Association 215, no. 7 (October 1, 1999): 992-999.
    5. Muñana, K R, D Zhang, and E E Patterson. “Placebo Effect in Canine Epilepsy Trials.” Journal of Veterinary Internal Medicine / American College of Veterinary Internal Medicine (November 11, 2009).
  3. Internet blogs discussing the placebo effect in animals. The comments of these blogs are worth reading.
  4. The mechanisms of the placebo effect
    1. de la Fuente-Fernández, Raúl, and A Jon Stoessl. “The biochemical bases of the placebo effect.” Science and Engineering Ethics 10, no. 1 (January 2004): 143-150.
    2. Haour, France. “[Mechanisms of placebo effect and of conditioning: neurobiological data in human and animals].” Médecine Sciences: M/S 21, no. 3 (March 2005): 315-319.
    3. Oken, Barry S. “Placebo effects: clinical aspects and neurobiology.” Brain: A Journal of Neurology 131, no. Pt 11 (November 2008): 2812-2823.
    4. Scott, David J, Christian S Stohler, Christine M Egnatuk, Heng Wang, Robert A Koeppe, and Jon-Kar Zubieta. “Individual differences in reward responding explain placebo-induced expectations and effects.” Neuron 55, no. 2 (July 19, 2007): 325-336.
    5. Scott, David J, Christian S Stohler, Christine M Egnatuk, Heng Wang, Robert A Koeppe, and Jon-Kar Zubieta. “Placebo and nocebo effects are defined by opposite opioid and dopaminergic responses.” Archives of General Psychiatry 65, no. 2 (February 2008): 220-231.
    6. Zubieta, Jon-Kar, and Christian S Stohler. “Neurobiological mechanisms of placebo responses.” Annals of the New York Academy of Sciences 1156 (March 2009): 198-210.

    This is a summary of some interesting findings including answering the question of whether drug addiction can be used to test the placebo effect:

    1. The placebo effect is observed in animals-there are studies done with different species.
    2. The placebo effect can be due to the way the animal owner treats the animal. That is, if the owner has an expectation of a treatment, he or she will act differently toward the animal.
    3. XJ’s idea of giving an addictive drug and then giving a fake drug to see if a high can be induced has some support in the literature. One study ( showed that one can induce expectation of treatment from arm pain with morphine. On the last day of treatment, a placebo is administered instead of morphine. The placebo treatment resulted in pain decrease. Thus, the experiment to test the placebo effect by using morphine could be done. However, in the reported study, morphine was used to decrease pain and not to induce a high. It remains to be seen whether a placebo can induce a high. However, a repeat of the linked study in primates or other animals could be done to test the placebo effect in animals.
    4. The number of studies done with the placebo effect in animals is quite small. There are many opportunities to study. One problem with using animals to study the placebo effect is that human symptoms such as pain or headaches or nausea can not be done with animals as animals can not tell the investigator what they are feeling.
    5. There is much work done on the mechanisms of the placebo effect which would be interesting to look at closely and compare them with drug addiction mechanisms. This comparison may be done in a future report.

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2 Responses

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  1. XJ says

    not conclusive.

  2. admin says

    Further work needs to be done clearly with all aspects of the placebo effect (which could be different in animals and humans). Is there some specific experiment that you would like to see that would be ‘conclusive’?

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