Many alternative therapies are known to act mostly or entirely as placebos. Acupuncture, homeopathy, and many popular nutraceuticals like glucosamine consistently fail to demonstrate benefits greater than placebos in controlled clinical studies. Yet because of their placebo effects, they often make people taking them feel that their symptoms are improved.
Much debate has occurred around the question of whether such non-specific actions are truly beneficial and whether it is appropriate to encourage or discourage patients from using therapies with primarily placebo effects. In the case of human beings, the perception of relief may be of some value even in the absence of true improvement in one’s physical health. Physicians differ in their opinions about whether the use of placebos, and the deception of the patient this activity entails
, is ethical in clinical practice. However, the terms and details of this debate are quite different when the doctors are veterinarians, like myself, and the patients are non-human animals.
Since placebos are generally thought to work by creating the false belief that one is getting an effective treatment, how can animals experience placebo effects when they do not appear to have explicit beliefs about their own health? Placebo effects are relevant to pets, and placebo-controlled studies are critical to an accurate understanding of whether medical therapies truly work for our animal companions.
The most significant aspect of placebo effects in animals is what is known as the caregiver placebo. Animals cannot directly report their subjective symptoms, such as pain or nausea, so veterinarians and owners must observe animal patients and decide whether they are responding to a medical therapy. Often, the humans will perceive improvement even when objective measures show none or when the animal is actually getting a placebo treatment.
Research has shown that in controlled studies of arthritis treatments in dogs, for example, veterinarians reported improvement 40-45% of the time, and owners up to 57% of the time, even when the dogs were actually getting a placebo. In practice, I see this often. Even when all objective measures of disease suggest a therapy isn’t working, owners who are hoping for the best will tend to see improvement in subjective symptoms of their animals. I presume that I am as susceptible to this as anyone else, so I likely see improvement where there is none as well, though obviously I don't see myself making this mistake or other cognitive mistakes. This is why I try to stick with evidence-based treatments and objective measures of response as far as possible in my clinical practice.
There are other reasons why ineffective or placebo therapies might appear to work in animals. As is the case with humans, when animals are in research studies, they tend to get overall better care and monitoring than when they are not. As a result, many patients show improvement even if they are on a placebo treatment. For this reason, if a study that shows benefits for a particular treatment doesn’t include a placebo control group, those results are not a reliable measure of whether that therapy actually works.
Natural improvement with time, misdiagnosis, the effects of multiple therapies given together, along with other factors, can make therapies appear to work even when they do not. This is especially likely when the measures of improvement are subjective and interpreted by the patients’ human caregivers or when the evidence is taken from anecdotes or sources with a vested interest in the treatment being studied. All of these sources of bias and error combine to create the false appearance of benefit from treatments that don’t actually work, which is the broadest definition of the placebo effect. In this sense, placebo effects definitely apply to animals even though they likely do not have beliefs about their own health.
The fact that placebo effects can mislead us when evaluating medical treatments for animals raises some important secondary issues. The most important from my perspective as a veterinarian is the ethical problem of utilizing treatments that make people feel better about their pets’ health without actually making the pets feel better.
I once saw a young Rottweiler with osteosarcoma, a very painful bone tumor. The owner was treating the dog’s symptoms with homeopathy, acupuncture, and herbal remedies managed by a veterinarian practicing Traditional Chinese Veterinary Medicine (TCVM). She consulted me about other options, but she chose not to pursue surgery, chemotherapy, or other conventional treatments, which were not likely to cure the dog. I did suggest, though, that since the dog was not walking on the affected leg and cried when it was touched, and since the evidence for veterinary homeopathy and acupuncture as pain relief is poor, we could try additional pain relief therapies. The owner was surprised and somewhat offended at my suggestion because she was certain that the treatments she was using were helping her dog. In situations like this, the caregiver placebo effect can lead to significant suffering for our animal companions.
The other ethical problem presented by utilizing placebo therapies in veterinary medicine is that we must deceive our clients in order to obtain even the indirect appearance of a benefit. Pet owners expect and deserve an honest appraisal of the scientific evidence for the recommendations we give them. Even though this evidence is often weak even for the best-studies therapies, we cannot ethically present treatments as known to be safe and effective based only on anecdotes or our own experience as vets. The evidence may be weaker than in human medicine, but the ethical standards aren’t.
Placebo effects, of course, operate for all medical therapies, effective or ineffective, conventional or alternative. But when considering alternative therapies, it is especially important to be aware of such effects because these therapies usually lack convincing scientific evidence that they have benefits beyond that of a placebo. As mentioned, uncommon alternative therapies like acupuncture and homeopathy are no better validated scientifically for pets than for people. Even some of the most commonly used therapies, like glucosamine, which is ubiquitous in the treatment of arthritis in old dogs and cats, often lack any reliable evidence they actually help.
Because the false impression of a benefit from an ineffective therapy can truly harm our animal companions, who cannot speak for themselves or tell us directly when we have failed to relieve their symptoms, it is especially important to insist on reliable, controlled scientific evidence for the safety and efficacy of the therapies we use for our pets.