Sugar Pills For Dogs

James herriot

If my patients could talk there’s just one thing I wish they’d mentioned to me sooner…there is a placebo effect in animals.

The placebo effect is any effect a treatment has that is not due to its medical properties. For example a person who takes a sugar pill and is told it is a new treatment for arthritis may sometimes feel a reduction in their pain levels even though the pill has no true medical effect on them. This will be due to a variety of factors but is unlikely to be due to the fact that sugar pills are particularly good painkillers.

The placebo effect is also used in research. Good clinical trials will include a group of people receiving a placebo treatment so that any beneficial effects from a new drug or medical procedure can be compared against the placebo group. This means you can be more certain that your new cutting edge treatment is effective due to its medical properties and not due simply to the placebo effect.

I always wrongly assumed that animals, who have no concept of, “I am taking these tablets and they might make me feel better,” would be immune to this effect. As it turns out, this is not the case. Why is this?


The effect of conditioning in animals was first studied by Pavlov in the 1920’s. He discovered that dogs could develop a learned physiological response to certain stimuli. The most famous of his experiments involved ringing a bell just before dogs were fed. Eventually the dogs started to associate the sound of the bell with the imminent arrival of food and they would begin to salivate whenever the bell was rung, even in the absence of their dinner.

pavlovs dog

Dogs, rats and even guinea pigs have been shown to develop powerful conditioned responses to medical interventions. Dogs that were given daily injections of morphine which caused them to vomit and become sleepy eventually showed these signs even when they were only given injections of salt water. Guinea pigs were even conditioned to produce an immune reaction in response to being scratched on the back of the neck after being given repeated injections of bacteria at the same time as their neck was being scratched.


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Animals that feel they have some control over their environment and can get away from painful stimuli are happier. That part seems obvious, but these animals are also healthier too. Inescapable stress has been shown to suppress the immune system and even lead to faster tumour growth. Animals can be conditioned to expect certain things from a treatment and this can give them a sense of expectancy and therefore control. For example if every time a dog goes to the vets it is given a shot of pain killer, it will begin to associate a trip to the surgery with relief of pain. This expectancy of relief from stress every time it goes to the vets can then have a beneficial effect on its health.

Incidentally conditioning and expectancy are the reason myself and many other vets like to bribe puppies with treats when they come in for their first few vets visits. We want them to associate us with something positive and give them the expectancy that the vets is a nice fun place to go (how long this illusion lasts is variable!).

Human Contact

It seems that the animal-human bond can be mutually beneficial. It is well known that owning a pet has been shown to decrease our own stress levels but human contact has also been shown to have some benefits for our furry friends. Petting by humans has been shown to decrease heart rate in dogs and horses, it has also been shown to have effects on blood pressure and aortic and coronary blood flow in dogs. Animals that are receiving treatment often get more human contact and this may have a beneficial effect.

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My notable exception would be cats on tablets, I am not sure retrieving them from behind the sofa or up the curtains whilst they repeatedly spit out their medication will have the same effect on heart rate or blood flow as a nice cuddle!

Other Effects

There are three other main reasons other than the placebo effect why an animal would improve on a particular treatment…

  • The treatment actually works.
  • Natural resolution; the disease was going to get better anyway and it’s just coincidence that this happened at the same time the treatment was given.
  • Regression to the mean; biological variables naturally fluctuate over time around an average value (the mean). Change in one of these values may be interpreted as an improvement in a disease process when it is actually part of this natural fluctuation.

All of this shows why good placebo controlled clinical trials are just as important in veterinary medicine as they are in human medicine.

dog labcoat

It also shows that interacting with your pet can be good for both of you so go find your favourite furry, scaly or feathery friend and give them a bit of love.

2 Responses to “Sugar Pills For Dogs”
  1. Ash says:

    Another thing worth mentioning, I think, is the effect of giving the medication on the owner’s perception of the disease.
    I don’t know if this has ever been proven reliably, but I see it regularly. Owners often appear to feel that their pets’ condition is improving, in the absence of any real progress, simply because they believe the treatment is working.
    ”He’s definitely starting putting weight back on now he’s on the tablets!” – turns out the cat is skinnier.
    ”She is walking so much better since the meds started!” – as the ageing dog drags herself through the door and slums in a creaking heap.

    • ellen says:

      I also see this regularly, the effect is known as the caregiver placebo effect where the caregiver believes that their charge is getting better purely because they are on some kind of medication. apparently even vets can be susceptible to this. It has been extensively studied in paediatrics and to a lesser extent in veterinary medicine.
      If you want an excellent paper on the subject in veterinary patients look at CONZEMIUS, M.G. & EVANS, R.B. (2012) Caregiver placebo effect for dogs with lameness from osteoarthritis. JAVMA 241(10), 1314-1319.

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