The placebo effect is a phenomenon that we generally tend to relate to the human being, since in order for this to be possible it is necessary for certain cognitive capacities to exist that we generally assume do not exist in other beings. In order for this effect to occur, it is essential that the perception or idea that a specific stimulation is going to generate a specific effect on a specific problem is given, something that requires complex processing of information, both internal and external.

However, the truth is that we are not the only beings who have manifested to be benefited by this effect. That is, there is the placebo effect in animals , which we will talk about throughout this article.

What is the placebo effect?

Before delving into the possibility of finding the placebo effect in non-human animals, it is necessary to briefly clarify what we call the placebo effect.

A placebo effect is understood as a situation in which an individual with a certain problem presents an improvement in the symptomatology that is attributed to the effects of a supposed medication or treatment that is considered to produce such an improvement, despite the fact that the treatment itself does not actually have any therapeutic effect on the problem .

We would therefore be faced with an improvement generated by self-suggestion, in the belief that following the treatment must or will produce specific effects on our health.
This is not an illusion or a false perception , but the improvement is generally real and palpable for the patient, but it is the product of the action of the mind on the body and not the effects of a specific drug or intervention.

Why is it considered humane?

Based on the above definition, we can understand why at a popular level we tend to think of the placebo effect as something specific and unique to human beings: being able to imagine that a particular substance or intervention is going to improve us from an ailment implies identifying both the ailment and the substance/intervention and generating the belief and expectation that taking the substance will eliminate or reduce the ailment we suffer from.

That is, it requires a certain capacity of imagination, planning and abstraction when projecting positive properties to the substance itself for the concrete situation we are in. It also requires the ability to make expectations about the possibility of recovery.

The placebo effect in animals

The large number of cognitive abilities that are assumed to be necessary and essential for the emergence of the placebo effect clashes head-on with the traditional perspective that sees the rest of the animals as beings with lesser cognitive abilities , which is why it is not generally thought that it can occur in animals. But the truth is that it does.

It has been shown experimentally with different animals, including dogs, that the provision of certain care and completely harmless substances can have a positive effect on the immune system, through case-control studies.

In situations where one group of animals was treated for a particular disease with one drug and others with a placebo, improvements were seen in both groups (obviously greater in the group treated with the actual drug). This improvement was objectified with different measures, independent of the subjective assessment of owners or veterinarians . There are multiple disorders in which this effect can be observed, and it can even generate slowdowns in the growth of tumours.

There are multiple possible explanations for this fact, with different authors having developed various theories and models in this regard. The following are some of them, being especially in the first two cases some of the most accepted.

The theory of classical conditioning

The causes of the placebo effect in animals, and in fact also in humans, can in fact be based on the conditioning acquired from previous experiences : if an animal (or person) associates that taking a substance with certain characteristics has generated a particular effect in his organism (for example feeling calmer after drinking a liquid of a certain colour or taking something similar to a pill), the subject in question will come to assimilate the improvement with the stimulation in such a way that he will tend to believe that he will improve in the future.

This is something that happens in the human being when we take a pill that is given to us in a state of pain: in a short time the pain is reduced because we have assimilated that said pill will make like drugs that we have taken previously (for example the typical Gelocatil).

The same is true for animals: if swallowing a pill is repeatedly associated with feeling better , in another situation where the animal feels bad, it can expect such an effect from a pill. This does not mean that they will swallow it (this would involve variables such as whether they dislike the bad taste or texture, or relate the pill to its owner forcing it on them).

Cognitive model: expectations

Probably the model that has had the most difficulty in being applied to non-human animals is the one that refers to expectations, which are linked to a symbolic capacity that animals are not considered to possess. However, although the cognitive capacity of each species is different, it has been observed in different beings that it is possible to create expectations and sensations of the capacity to control or not control situations , as well as the existence of learning when faced with stimulation.

The most obvious example (although it would be rather the opposite of the placebo effect, the implications are the same) is that of learned helplessness: doing nothing to avoid something because one’s own behaviour is expected to have no effect. This is typical of depressed subjects (both human and animal), which in turn leads to a decrease in the body’s defenses. The opposite situation would generate, on the contrary, an increase in the tone of the immune system and a greater capacity to recover from the disease.

The effect of stress

Another possible reason why the placebo effect may appear is because of the reduction of stress in the face of the disease. Taking a drug or the activities or treatments carried out during a treatment (including trying to pet them, calm them down, etc.) can reduce the stress level of the animals that follow them. Since stress has been shown to be an important risk factor and worsens the condition of sick subjects, the treatment could generate a relief of such stress which in turn would generate a symptomatic improvement.

This effect would also be linked to an effect that has also been observed: positive physical contact with an animal results in a more resistant state of health and an improved immune system, just as contact with animals is often a positive factor in the improvement of various physical and mental diseases and disorders in humans.

A theory not yet extrapolated to animals: the role of endogenous opioids

It has been observed that the perception of different degrees of discomfort, pain and physical discomfort can be greatly diminished in humans by the action of endorphins or endogenous opioids .

However, although many animals also have such substances in their nervous systems, little testing has been done on them, so this is theoretical.

Placebo by proxy

The placebo effect in animals exists and it is something that has been demonstrated, but the truth is that it has also been observed that in some cases, as we have previously insinuated, a situation can occur in which something that is not a placebo effect is interpreted, which would be known as a placebo by proxy: the animal in question does not present a variation in its symptomatology, but the people who observe it do believe that this has occurred because they have been given a specific treatment .

This type of placebo is especially given to pet owners, who are reassured that they have provided some form of treatment to their animal companion and perceive it as better than before even though there may have been no improvement in their condition.

Another situation could be the opposite: a sick pet, perceiving that his human companion is nervous or upset by his condition, could become restless and upset to a greater extent than his problem would generate. When the human being in charge receives a treatment and is reassured , this reassurance could relax the animal’s state of disturbance and also produce an improvement. This would be a somewhat different type of placebo.

Bibliographic references:

  • McMillan, F.D. (1999) The placebo effect in animals. JAVMA, 215 (7): 992-999.