Mercury Poisoning in Cats

Picture of a black and white cat

Severe mercury poisoning cases in either cats or dogs have decreased in the past years mostly because people have started to use electric thermometers instead of old-fashioned ones.

However, cats can also develop mercury poisoning from fish or even commercial pet food if it has been contaminated with this metal. In today’s post, we are looking at everything you should know about this health issue, from its causes and symptoms to how it can be treated and prevented.

What causes mercury poisoning in cats?

One of the main causes of mercury poisoning used to be the use of vintage thermometers, which contained this heavy metal. For this reason, these devices needed to be handled with care by people so as not to drop them on the floor.

Mercury is extremely toxic when inhaled or ingested in its original form. The worst thing about it is that it spreads into very, very small parts across the floor if you make the mistake of breaking a thermometer, for example.

However, since these days people use digital thermometers, which are capable of measuring the temperature of a person’s or pet’s body without needing mercury, this cause is less frequent.

What is nowadays at the root of mercury poisoning cases in cats is feeding them oceanic fish time and again. We all know how cats love their fish, and you might not think that they contain massive amounts of mercury, but you can’t say for sure. Even the cat food that you give your friend can have traces of mercury, which can accumulate in their body gradually.

The worst part is that there are now no standards with regard to how much mercury should be in pet food. Because of this, the best way of preventing mercury poisoning in your own cat would be to give her fish pet food or actual fish that you intend to prepare for yourself so that it makes up less than 10% of their diet.


Most of the clinical signs associated with this health problem involve the nervous system. As such, you might notice the following:

  • Incoordination
  • Rapid eye movements
  • Partial paralysis
  • Vision loss
  • Wobbly walking
  • Loss of coordination
  • Tremors and sometimes even seizures
  • Meowling or howling continuously
  • Hiding in dark places
  • Involuntary movements

The biggest issue with these symptoms is that they aren’t necessarily specific to mercury poisoning. They can also be signs of brain or nervous system tumors, intoxication, or a severe lack of vitamin B1.

Your veterinarian can recommend a number of tests that can lead to a correct diagnosis, such as urinalysis, where the presence of mercury might be revealed. Sometimes, collecting a small tissue from the kidneys might be necessary, much like a biopsy.

Concentrations of mercury of less than .1 mg/kg in both your cat’s body and in your cat’s food are considered more or less normal. Poisoning can occur when a level of more than 5 or 6 mg per kg is discovered. When more than 10mg of mercury is found in the kidney or .5 mg/kg in the brain, the diagnosis is quite clear.

Additional testing that can reveal the presence of protein in the patient’s urine or inexplicable anemia might lead to the same diagnosis.


Treating this type of intoxication is extremely challenging and, in some cases, might not even be recommended.

If you know for a fact that your cat ingested a battery or the contents of an old-fashioned thermometer, the best thing would be for you to take them to the vet clinic as early as possible so that the vet can at least administer activated charcoal to limit the absorption of mercury into your pet’s blood flow.

Some damage might also be limited through the administration of selenium or vitamin E. Moreover, medication against kidney disease needs to be given to the cat even before the mercury has gotten into their blood flow – because the damage that this metal can inflict on the renal tissue is very fast and severe.

Can cats recover from mercury poisoning?

It depends on every case in part. If your cat has gradually developed mercury poisoning but not to the extent that their brain or kidneys were severely damaged, some supportive therapy might be helpful.

In severe intoxication cases, such as when the cat ingests the contents of a thermometer or a battery and the animal doesn’t receive veterinary assistance right away, they can lose their life. The other possibility would be to limit the absorption of mercury, but sometimes that might be impossible in a complete manner, which is why the cat might experience kidney and brain damage with the related symptoms.

Preventing mercury poisoning

The first and obvious piece of advice that we can give you is to replace your thermometers with electronic ones as soon as possible. If you can’t do this, just make sure you keep your old thermometers in safe places to which your cat has no access.

Also, when removing batteries from your devices, always do it when your cat is not around.

As for the mercury poisoning that can be developed as a result of your cat’s food, you can feed your pet fresh fish every now and then, but you should only do it once a week or less. The amounts need to be limited, too.

Even commercial pet food that has fish as an ingredient needs to be limited. Although your cat might love it, it’s just not worth the risk, so think of it more as a snack rather than the main food source.


Mercury Poisoning in Animals, Barry R. Blakley, MSD Veterinary Manual, 2021



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