The placebo effect is usually viewed as a treatment of faith. If you believe the pill will help you, it will; the only condition is that you must believe it. In this light, it is plausible to dismiss the notion of Placebo having an effect on animals, especially pets in veterinary medicine.

After all, cats and dogs can’t possibly be informed about how good the homeopathic remedy or spiritual healing might be; thus, if they work on dogs or cats, it can’t be placebo. But can it?

In this article, you will learn how placebo affects animals, what else is hiding behind placebo’s therapeutic effects, and whether we can use the magic power of placebo to treat our pets—dogs, cats, and others.

Do animals respond to placebo?

Straightforward answer first—yes, placebo DOES affect animals.

That’s right. While it indeed seems that consciousness is important for the placebo effect to manifest itself, at the same time, this conscious thought is not all that there is to it.

Placebo is much more, and at the same time, much less than the average person understands of it. How can this be? We’ll dive into that later. But first…

Regardless of the questions of how and why, there is a significant amount of evidence supporting the conclusion that the placebo effect is present in veterinary medicine.

Placebo responses have been observed in various animals: rats, dogs, monkeys, horses, and others. It is recognized well enough that placebo control is included in trials of new veterinary drugs for one simple reason—animals do respond to placebo.

But how does this happen? If placebo is administered to an unsuspecting dog, how can he possibly expect to (and actually) get better from it? The first reason is because placebo is not only in the mind. It also works inside the body. Second, saying that a pet cannot possibly understand that he is being treated is an underestimation of pets’ cognitive abilities (at least in most cases).

How does placebo work?

Here are a few suggested theories regarding how placebo in human medicine is explained. You will see that these ideas are all totally valid for pets, as well:

• Classical conditioning. A remarkable demonstration of a placebo-like effect in pets was shown by Dr. Krylov in the early 20th century. A dog was regularly injected with morphine (testing of animals was viewed radically differently back then), and after just few days, the dog showed negative side effects of morphine injection (vomiting, dizziness, etc.) whenever the animal arrived in the procedure room, even without receiving the injection. In this case, not the mind but rather the immune system of the dog learned to react accordingly when it predicted morphine coming. In a similar way, the body can learn to react to medication in many different ways. For example, the first injection puppies and kittens normally get is their first vaccine, and a booster is given again a few months later. It’s not only about the injection; every detail, including the scent of the veterinary clinic, sound of a medicine bottle opening, and even an owner getting nervous before a visit, can contribute to the pet’s body “learning” that the immune system needs to be activated. Beyond this example, there are many ways that a pet’s or person’s body, without being conscious of it, can “learn” that getting an injection, taking a pill, or getting a surgery means it’s time to start self-repair.
• Expectation of getting better. If you know that you will get better, you will get better; that is how most people understand placebo, and it applies to animals too. For example, if a dog gets a pain killer injection, it usually kicks in rapidly, and there is nothing to stop him from connecting the two events. That is one thing. It is also demonstrated that a pet owner’s expectations about the treatment can have an impact on the outcome. On one hand, this is because optimistic owners may be more precise in following a veterinarian’s instructions. On the other hand, it is known that an owner’s stress can be translated to pets, and there is no reason to think that the opposite (optimism, or the lack of stress) wouldn’t transfer in kind.
• Human contact. While it’s under debate that the positive attitude of medical staff in human healthcare could have significant influence on recovery, different health benefits from human contact (such as lowered heart rate or blood pressure) have been demonstrated in animals, ranging from dogs and horses to monkeys and rats. On the surface, it seems plausible that petting and gentle handling is able to reduce the stress of an animal and therefore benefit its health, but even more surprising, similar effects have been observed in cases when the encounter with humans isn’t at all pleasant—such as receiving an injection in a veterinary clinic. A vet visit is rarely a positive experience for pets.

When you look at the above suggested mechanisms of how a placebo might work, it is clear that most of them stand on plausible ground, and they are not mutually exclusive. While classical conditioning contributes most, all of the above appear to chip in their contribution to the grand total of the placebo effect in both human and veterinary medicine.

But that is only a part of the story.

Is placebo always a placebo?

Placebo isn’t always what you think it is. We have already explained why it is more than most of you thought before; at the same time, placebo is also less than what the majority thinks it is.

In general, if a patient gets better when using drugs with no active ingredient (or without a helpful active ingredient), it is recognized as a placebo. But it doesn’t have to be.

Here are few examples of when placebo isn’t really placebo:

• Regression to the mean. Patients with chronic problems tend to get better and worse all the time. There are good days, bad days, and normal days comprising the majority of days. A medicine is usually given on bad days, obviously. That means the next day, on average, is more likely to be a better one, regardless of the treatment. It would have come anyway, but a patient will experience “an improvement” after taking a pill.
  
• Biased conclusions. We and our clever human brains are very good at misconstruing our conclusions about almost anything. We tend to remember good things more vividly and shrug off bad ones as irrelevant. That means, for example, if a pet owner treats his dog’s arthritis with homeopathy, he is likely to remember every time in which his dog got better after the treatment but write off as irrelevant all those times when improvement did not follow. Even if the treatment helps only half of the times, he will conclude that it works. If you think this is limited to pet owners, think again. Academics are also guilty of distorting reports (both consciously or unconsciously) on drug trials and other research pieces.
• Natural resolution. Not all medical conditions require active treatment. Some just need to rest or remove the root cause. In human medicine, there is a joke that if you treat the common cold, it will go away in a week, but if you do not, you will be well again after only seven days. That is why the common cold is very adaptive to placebo treatments—it tends to resolve by itself. There are numerous problems that the body is able to get hold of all alone, and often they are misleadingly attributed to placebo.
• Non-specific effects of the treatment. In certain cases, it may happen that the treatment of choice indeed does help the patient to recover, but not in a way that is expected. The most banal example is if you treat dehydration with magnesium pills. Magnesium does not affect hydration, but the water you drink while taking the pills does.

All in all, we are not here on a mission to destroy placebo or alternative medicine. We want to demonstrate that placebo and placebo-like effects, as described above, are not limited to the human mind and do not require a patient consciously knowing that the treatment will help.

Is the placebo effect an unresearched magic cure?

Finally, there is still one thing that cannot be left unattended. Can placebo provide a whole new area in which doctors could work? Can we treat humans—and can we treat our pets—using the magic powers of placebo?

It sounds extremely tempting. What about an easy to administer, cheap medicine that delivers the cure just as well as conventional drugs (which seems sarcastic, given that drugs are, by default, recognized only when they perform significantly better than placebo) but conveys no adverse effects at all?

Cancer treatment without chemotherapy? Effective pain killers without damage to internal organs?

Sounds good, but if it really is possible, we aren’t there yet.  As it is now, placebo is unlikely to cure a disease completely on its own. Will it ever?

Some studies show that placebo is as “good” as not treating at all. Others suggest that placebo is getting stronger over time, which might be either because people nowadays expect more from treatments (better expectation should equal stronger placebo response) or because the clinical trials have attained higher quality (a low-quality trial is likely to exaggerate the effect of the investigated drug and belittle the effect of placebo).

The sad truth is that when we strip the placebo effect from all the other things it is surrounded by—regression to the mean, investigator bias, natural resolution—there isn’t much left.

That being said, however, it does not mean that the placebo effect shouldn’t be explored and maximized when possible.

Since it is observed in pets, veterinarians could benefit their patients by understanding how placebo (and all the things that appear as placebo) work. For example, if we know that a dog’s body can learn to react to morphine without morphine, it is easy to wonder what else can it learn to react to.

At the same time, relying solely on placebo is simply unethical if there is an effective medicine available. If there isn’t, that might turn out to be a different story.