The Placebo Effect in Animals: Fact or Fiction?

What is the placebo effect in animals?

The placebo effect is a beneficial effect produced by a substance which can't be a result of the substance itself.  Instead the effect is caused by the patients belief that the placebo treatment is working.  Our dogs and cats can't know that a treatment is supposed to be making them feel better so is the placebo effect in animals a real thing?


Lets start with the answer and then discuss the placebo effect in animals in more detail.  Quite simply, there is no such thing as a true placebo effect in animals.  Our dogs and cats can't possibly know a particular intervention is designed to make them feel better.  Therefore no placebo effect can be generated.

Does this mean that all studies or anecdotes (personal accounts detailing the results of a treatment given) that show a positive result to a given treatment should be believed, and held up as proof that the treatment works?  Of course not!

Caregiver placebo in owners (and vets!)

There are 2 main theories that can quite successfully explain why a placebo-like effect can be seen in animals.  The first of these is caregiver placebo, also known as placebo by proxy.

Picture the scene, your pet is unwell, is in pain or has something that you are worried about.  You want them to get better and so seek help.  This could be from your veterinarian but could just as equally be from a friend, internet forum or any other source of advice you might choose.  Some questions are asked, an examination is carried out, some tests might even be run and the treatment or management plan is given.

By this stage you have invested time, emotional energy and potentially a lot of money depending on the condition.  The likely expectation is that the treatment advised will make your pet feel better and recover from whatever condition they are suffering from.

Because we are so invested in our pet, we really want to see them improve and likely believe the treatment will work.  We, as the pet owner, are highly susceptible to caregiver placebo as a result.

There is a real risk we will see improvement even when it is not there.

The caregiver placebo effect in animals means we can see improvement even when none is present

It's not just owners who can suffer from caregiver placebo.  As a vet, I am all too aware that my desire to see a patient of mine improve, coupled with the belief that the treatment I am prescribing will help, makes me just as susceptible to caregiver placebo.  The same goes for anyone involved in that pets care.

So caregiver placebo can mean that we see an improvement in our pets condition even when our pet is not actually experiencing any improvement themselves.

Don't believe this is the case?  Well it is clearly shown in one study where the opinion of the lameness of a patient by owner and veterinarian was compared against how much force the dog was actually putting through its legs.  This would be on objective, true assessment of the dogs lameness.  In around 40% of instances, the owner and vet felt there was an improvement, even when none was present.  In fact the vets were a little worse than the owners!

Just because we believe a treatment is helping our pet doesn't mean it actually is!

This caregiver placebo effect is one very important reason that treatment trials have a placebo group, even when we are evaluating the effect of a treatment in animals rather than humans.  It is also one reason why anecdotal reports, that is individual stories of successful (or unsuccessful) outcomes are a really poor form of evidence.

I'll actually discuss the various forms of evidence and studies in a later article as well as addressing some other reasons why treatment we give our pets may appear to make them better when in fact they are not making a difference.

Regression to the mean

This is another reason why a treatment might appear to be working when it actually isn't.  Might your dog or cat get better despite what they are given rather than because of it?  This is different to caregiver placebo because your pet will actually be getting better.  However, all might not be as it seems!


Regression to the mean is a simple concept that can bring into doubt the fact that a particular treatment or intervention helps cure or manage the illness it is proposed to help.  You may have even seen a dramatic improvement in your pet that was not just wishful thinking or caregiver placebo. The improvement was real.

Why then should you still question if a treatment works or not?

Many disease, especially chronic, long standing diseases, wax and wane in their severity.  They slowly get worse, reach a peak and then slowly improve. If we take arthritis as an example, an arthritic dog or cat will have periods where they seem relatively comfortable (or at least less painful).  Conversely there will be times where they seem to be struggling or suffer from a sudden, acute flare up in symptoms.

The average level of pain they are in is called the mean.

Knowing this, let’s do a little thought experiment.  Your pet is the arthritis dog or cat we are talking about.  They are not yet on any treatment. When do you think it is most likely that you will take them to the vet or start some other form of treatment?

I imagine you answered that you would seek advice when they were at their worst or thereabouts.  When they are at their most painful is when an intervention is given. That might be starting them on an anti-inflammatory painkiller.  It might be giving a joint supplement like glucosamine.

What happens next is that their pain levels decrease.  They are happier and more mobile.

But did your intervention actually make any difference?

Let’s go back to the fluctuating symptoms of chronic disease.  When our patients are at their worst, there is only one way their symptoms are going to go.  They are going to return to the average, or mean. They are going to improve to some degree whether you do anything or not.

This regression to the mean is another reason why treatment studies should include both a treatment group and a “placebo” group.  Both groups will have a tendency to get better as a result of regression to the mean (patients that are enrolled in studies are often at the worse end of the spectrum which is what encourages them to enroll in the first place!).

It is only by comparing the two groups that the actual efficacy of the proposed treatment can be evaluated.

So next time your dog or cat is feeling under the weather (or yourself for that matter), and you try the latest, greatest treatment or supplement out there, ask yourself if they are getting better because of you or in spite of you.  This is certainly a question I regularly ask myself!

It is these very effects which are likely responsible for much of the improvement claimed by many alternative therapies, that time and again have been proven not to work in better designed studies.

If you don't think a treatment will work, you might not believe it has!

Could the reverse of caregiver placebo also be true?  Absolutely.  If we believe that a specific intervention is going to make no difference, or may even harm our pet, there is a reasonable chance that we will fail to notice any improvement that might take place.

Evidence based veterinary medicine matters

Evaluating what works and what doesn't is a vital part of the progress of treatment of both humans and our pets.  Without evaluating the evidence in a proper, scientific way we might still be resorting to subjecting ourselves to regular bleeding sessions for every ailment and we may not even be washing our hands before surgery.

evidence matter in veterinary medicine. Just because we believe a treatment is helping our pet doesn't mean it actually is, the caregiver placebo effect is one reason for this

These ridiculous situations were the normal practices not all that long ago and it is only through proper evaluation of the information available to us that we can continue to improve our health care and live healthier, happier lives.

As evidence changes and improves, so to should our pet health treatment and management recommendations.

Our Pets Health: the best care for every pet, with every condition, every time