Pet Poison: How do I tell if it’s toxic?

Everything is toxic??

Let’s talk about toxicity as we move on to more complicated topics in pet poison.

The word “toxic” can be confusing

There is not a substance on Earth that’s entirely non-toxic, not even water! This means that any substance can be dangerous based on how much you’re exposed to. If someone claims otherwise, they’re either uninformed or trying to sell you something! Even the oxygen we breathe will harm our cells over time, ultimately leading to death. Toxicologists refer to “toxicity” to describe the level of danger in any given substance.

How do we determine the toxicity of any pet poison?

These are the main terms that describe the “toxicity” of a substance:


This abbreviation stands for “Lethal dose”. This dose killed 50% of a test population in a lab (usually mice or rats). For example, 30 out of 60 test subjects died after the administration of the LD50.

  • The LD50 gives you a rough indication of the dose size with a high death probability. To clarify, any animal that swallows a dose equal to the LD50 is at significant risk.
  • The LOWEST dose that caused death is lower than the LD50.  This dose is called the lowest lethal dose. Companies do not often report this dose to the public. Collecting this data accurately takes longer than determining LD50.
  • The information insert of prescription medications contains the LD50. For other chemicals or over-the-counter medications, the government requires companies to provide Safety Data Sheet (SDS) or Material Safety Data Sheet (MSDS).  Search for these on the internet to find the reported LD50 (Google: ibuprofen MSDS).

Margin of Safety or Therapeutic Index 

The margin of safety is a more fluid concept. It indicates the difference between a safe dose and a dangerous dose.  Mathematically, the margin of safety can be found by dividing the lethal dose by the therapeutic dose (or effective dose) of any substance.  Alternatively, you simply compare the difference between the two. The medical field defines this as the difference between the therapeutic dose and the dose known to cause severe signs.  Dangerous substances have a smaller difference. Comparatively, a safer substance has a larger difference between those doses.  Toxicologists call this margin either “narrow” or “wide” depending on the size of this number.

  • A wide margin of safety indicates that more of a chemical causes death, thus it is safer. A medicine that relieves pain with one pill and only causes severe signs after 60,000 pills has a very wide margin of safety.
  • A narrow margin of safety indicates that it takes less of a chemical to cause death, thus it is more dangerous.  A medicine that relieves pain after 1 pill and causes severe signs with 1.5 pills has a narrow margin of safety.


When analyzing mixtures of chemicals like cleaners, paints, and ointments, we use the concentration of a chemical. Calculating the dose of a compound medication is straightforward, but it becomes difficult with mixed liquid chemicals. Instead, we check the ingredient’s concentration percentage in the formula, which can be found on the MSDS.

For instance, let’s compare pure bleach to a household cleaner containing bleach. Pure bleach is 100% concentrated sodium hypochlorite, while a bleach-containing cleaner has varying amounts of bleach. A formula with 0.005% bleach is not highly concentrated.

To determine the concentration, divide the amount of an ingredient by the total liquid amount. If you mix one gallon of bleach with one gallon of water, the concentration is 1/2 or 50%.

Concentration amounts explain why animals can ingest paint with antifreeze and remain unharmed, but the same animal licking antifreeze from a garage can die. It’s also why certain chemicals in a formula can alarm some owners, but will not frighten doctors or veterinarians. The mere presence of a chemical in a product doesn’t imply the product’s toxicity.

How do these terms help us determine toxicity?

What is poison?

There is wiggle room in the definition of “toxicity” in a pet poison.  So, here are some broad rules of thumb that help us:

  • A dangerous pet poison will have
    • A low LD50
    • A small “lowest lethal dose”
    • A narrow margin of safety
    • A high concentration of a dangerous chemical
  • A safe substance will have
    • A high LD50
    • A large “lowest lethal dose”
    • A wide margin of safety
    • A low concentration of a dangerous chemical

Do I need to know these things if I own a pet?

While it is helpful and important for a pet owner to have knowledge regarding pet poison, The average pet parent doesn’t have to know these facts off-hand. Animal toxicologists exist to analyze these risks and make judgment calls when a case is not cut and dry.

In conclusion, if you are concerned about bringing any product, plant, or medication into your home, speak to your vet or call animal poison control! They are often happy to give precautionary information for free before an animal is accidentally exposed.

26 thoughts on “Pet Poison: How do I tell if it’s toxic?

  • Not everything is harmful but many things are. One thing not to forget is that natural doesn’t automatically mean safe.

  • Great post! I’m a total paranoid pet parent – I spend a lot of time researching new products before I’ll use them for/around my pets and I’m no stranger to my pet’s vets, who I often call for advice. Better to be safe than sorry.

  • Very good information here, thank you! I was not aware of some of those terms, so this is really good to know.

  • Things in moderation right? Mr. N only really eats food (meat in his mind) so the main thing we have to look out for are chicken bones!

  • It is important to read labels on any products that we use around our pets. Thanks for the info.

  • This is really good to know! Lots of things can definitely be harmful and the more we know the better we can be about making sure our pets are safe!

  • Great post. I am a label reader, but I am also aware that natural doesn’t necessarily mean safe either.

  • So important – there are so many cleaners that I thought were toxic but then understanding the level of toxicity and concentration is key. Great tips and education overall.

  • I always enjoy reading your posts because I learn so much. You make an excellent point about toxicity and it’s something that I don’t always remember in terms of concentration. I also really appreciate your breakdown for understanding the margin of safety.

  • Very interesting. You could spend so much time worrying. Kilo is a very greedy resourceful Pug and has had multiple calls to ASPCA poison control- love them and they have great data. So far only one vet treatment required after a dark chocolate and walnut binge (I blamed my hubby for leaving the brownies in reach) and he seems fine. We are very careful now.

  • Very interesting post! Great information which I am definitely going to share. Thank you.

  • Thank you for the information. I watch everything I use around the house to make sure it’s safe for the girls.

  • Wondeful info here! It’s definitely ver good to know. Thanks for sharing.

  • I try to avoid things that are highly toxic and I also try to keep all cleaning supplies, medications, and food where the dogs cannot get them.

  • Better to be safe than sorry. Thanks for sharing this valuable information with pet parents.

  • Interesting, I feel lucky that my animals don’t eat anything weird, but I do worry about things like bug spray that they could be exposed to. I’m thinking it also makes a difference if they’re big or small, right?

    • Yes! Size is a big part of dose. Insect sprays usually end up being either no big deal or really toxic. There doesn’t seem to be an in between!

  • This is very helpful to dispel / interpret some of the FUD!!!

  • This is really interesting! I have heard of these measurements before. They have come up in conversations about medicines that I have taken. It is really interesting how different an animal’s (or a human’s) body can react to different levels of a substance. Things can be both helpful and harmful depending on how they are used.


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