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Is it legal to give my cat over-the-counter painkillers?

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With the cost of living rising, seeking money saving options is something we are all trying to do. But, in short, you should never give your cat over-the-counter painkillers intended for human use, such as paracetamol or ibuprofen!

Below we will discuss why giving your pet cat over the counter painkillers is a very bad idea. And how it can end up costing you much more than initially seeking veterinary attention.

Over-the-counter medication is for humans. 

This medication has been trialled and tested millions of times on different humans to assess metabolism, toxic limitations, therapeutic thresholds plus many more vital pieces of information required in order for the medicine to be deemed safe to use. Even so, when painkillers are administered to humans, despite the vast amount of detailed information we have regarding the substance we are administering into our bodies, we never quite know how we will react. Some people have unknown allergies to common painkillers and may have adverse effects that your GP could not have predicted. Sometimes drugs may interact with other drugs within your body system – some drugs can even react with different foods. 

It must not be forgotten that, although these drugs are very easy to purchase, they should be used with caution. And only used once the person is aware of common side effects and potential risks associated with taking the medication. There are still risks when administering medications to humans, even after all health assessments on the drug have been passed. When it comes to cats, it is incredibly risky to give your pet an over-the-counter medication which has only been trialled on humans.

Cats and humans are very different

Remember, a cat is NOT just a human in a furry coat!

Size matters

For a start, cats are much smaller than humans so estimating an appropriate dose would be challenging. The difference between a safe dose and a lethal one can be very small in a 5kg cat compared to a 75kg human!

Different metabolism

More importantly, though, the metabolic processes available to a cat are very different to those of humans, or even dogs. Cats are obligate carnivores. As a result, however, they have lost much of their capacity to break down potentially harmful chemicals. (For those interested in the details, they have reduced cytochrome P450 activity compared to dogs or humans, and dramatically reduced transferase, especially glucuronidase, activity). This includes many medications which at normal doses can be broken down to harmlessness by humans and dogs, but not by cats.

Different blood

The red blood cells in your blood and a cat’s blood, look very similar, and have the same function. They contain haemoglobin to carry oxygen around the body. However, the haemoglobin in cat blood is very sensitive to being damaged by certain oxidant drugs. This means that many drugs that are relatively safe in humans can break down the cat’s haemoglobin; leaving them unable to transport oxygen, which is often rapidly fatal.

As a result, giving a medicine not intended for cats can result in a wide range of possible side effects; some of which are lethal.

Causing any harm to your pet could result in hospitalisation, intravenous fluids, further medication and diagnostic testing which can become very expensive, very quickly.

Veterinary painkillers

In order for painkillers to be prescribed to a cat, they must be prescribed by somebody suitably qualified to do so. Legally, that is limited to a vet. 

Prior to prescribing any drugs, your vet will want an up-to-date medical history and clinical examination, including weighing your cat. Your veterinary professional may advise blood tests to assess kidney and liver function, amongst other things, prior to prescribing medication. This is because selecting the wrong medication could exacerbate some disease processes, especially kidney or liver disease. It is also important that we understand why your cat is in pain and work out the problem; rather than just removing the symptom, as the underlying problem may continue to progress and get worse.

Complications from using human drugs in cats

There are a wide range of human painkillers that people may be tempted to give to cats. There are however good reasons why this is never a good idea.


Paracetamol is incredibly toxic to cats and should NEVER be given. There is no safe dose – even very small quantities can be fatal. Cats lack the ability to process paracetamol, so it builds up in their body. Paracetamol affects the oxygen carrying capability of the blood by destroying haemoglobin, resulting in “brown blood” (methaemoglobinaemia). It can cause serious liver disease too. If you have given your cat paracetamol, please contact your veterinary surgeon immediately. The sooner you can get your cat to the vets following administration of the medication, the better the prognosis for your cat is.

Anti-inflammatories (e.g. aspirin, ibuprofen, diclofenac)

Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspiring, ibuprofen, diclofenac, and many more, are widely used in human medicine. While we do use some specific NSAIDs in cats (meloxicam, carprofen, robenacoxib, for example), the doses are very carefully controlled and limited. We never use the major human drugs in cats because they do not tolerate them well. 

Clinical signs following administration of NSAIDs in cats include symptoms such as vomiting, decreased or no appetite, lethargy and diarrhoea; however, in most cases the main result is kidney failure. At very high doses, methaemoglobinaemia can occur, as discussed above. It is worth bearing in mind that half a normal (200mg) human tablet of ibuprofen can cause toxicity including renal damage to an average-sized cat.

What about prescribed painkillers?

When giving NSAIDs which have been prescribed to your cat, the vet will have worked out a safe dose of a relatively safe drug. Ensure you follow the safety precautions strictly. You should know exactly how much and how often you are dosing your cat. You should understand the method of administration, e.g. tablet or oral liquid, to ensure you are administering the medication correctly. If you have any concerns or uncertainty regarding your pet’s medication, give your vet a telephone call prior to giving your pet the product.

If your cat is in pain…

You should never administer over the counter pain relief to your pet cat. Off-licence products should only be used as a last resort, following a medication cascade process. This is where your veterinary professionals look at the research, licensing, the outcomes and the risks to decide which drug is most appropriate for your pet and change according to the symptoms and response. 

If you feel your cat is requiring pain relief, please seek veterinary attention as soon as possible. There is nothing safe you can do from home!

References and Further Reading:

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