We all know that there are several situations that would make us reach for a Benadryl or other antihistamine, almost without thinking. Hay fever; sneezing; runny, itchy eyes; insect bites; bee stings – the list goes on! So, when we see our beloved dog suffering the same kind of situations, can we simply do the same for them as we would for ourselves? 

The short answer is no! I understand that it is very tempting. And no one wants to be bothering their vet (or paying for a vet consult!) for things that can seem quite minor. But there are several good reasons why this is not necessarily the best idea. 

Firstly, giving your dog any medication without first speaking to your vet can be quite dangerous

At best, it can waste precious time when your pet could be getting the help that they need. You may be confident that you know what is causing your pet’s itchiness, sneezes, or hives. But the truth is there are several things that could be causing those symptoms. Like a potentially serious infection, or a foreign body like a grass seed in your pet’s skin or nose. The safest option by far is to take your dog to see your vet. They will be able to make a diagnosis. They are the best people to judge whether or not antihistamines are an appropriate treatment. 

Secondly, you may be surprised to learn that prescribing medicines to pets is tightly regulated by the Veterinary Medicines Directorate (VMD). 

All vets in the UK must prescribe medicines according to a system called the cascade. When a medicine has been tested and proven to work for a particular problem in a particular species, the company that makes the drug must apply for a licence to market and sell it. When the VMD has inspected the evidence that the drug company produces (the results of their research trials), they will grant the medicine a license. Which will detail which conditions this medicine can be used for and in which species. 

The cascade is a bit like a decision-making flow chart, which is legally binding. So vets can get into trouble if they don’t follow it. In addition, it is actually illegal for you to administer an off-license product without your vet’s authorisation.

The Cascade goes as follows:

  • Legally, when treating this condition in this species, the vet must reach for the drug that is licensed in the UK first. 
  • If there is no drug available for that condition in that species, or if there is a particular reason not to use that drug (for instance, that drug has already been tried and didn’t work, or the animal is allergic to that drug) then the next step is to use a drug that is licensed for that condition in that species in a different country. 
  • The next step is to use a drug that is licensed in the UK. But for a different species or condition. 
  • If there are still no suitable drugs available, the next step is to use a drug that is licensed in humans in the UK. 
  • Next, we can use a drug that has been specially prepared by a vet or pharmacist. 
  • Only as a last resort, can we use a drug that is licensed in humans outside of the UK. 

Benadryl, or any other antihistamine are not currently licensed in dogs or cats, but obviously are licensed in humans. 

You can see that this puts Benadryl at step 4 of the cascade

So legally it can not be the first thing that we reach for. Now, you may well find that your vet may prescribe antihistamines in certain situations. But that will be because they have assessed that they are the most appropriate treatment. And will have satisfied the rules of the cascade (ie. They will have a reason for not using a drug that is licensed for that situation).

Thirdly, giving your dog benadryl rather than speaking to your vet, is unlikely to be harmful but quite likely to be ineffective. 

Several studies have been carried out which show that antihistamines have, at best, very variable efficacy. One study showed that diphenhydramine (the active ingredient in Benadryl) had no effect at all in reducing allergic reactions in the skin of dogs. Another found that antihistamines had some efficacy in about 50% of dogs. But more often in milder cases and younger dogs. A large-scale evidence review showed no evidence that antihistamines are effective in dogs. Giving your dog a medication that may not work, will just result in them being uncomfortable for longer. And may result in the condition getting worse in the meantime. 

This doesn’t mean, that some dogs won’t respond well to antihistamines; there will certainly be cases where they are useful. And there will be times when it is completely appropriate for your vet to prescribe them. But, that needs to be decided in conjunction with your vet, after making a diagnosis and considering some other options first.

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