Antifreeze still poisons, even when it’s bittered

So, you have something that is sweet, tasty and tempting to sip from the bottle (or lick off the garage floor). But it’s also poisonous and can kill when ingested. It isn’t meant to be consumed anyway, so why not make it taste terrible instead? Problem solved!

Except it isn’t — at least not when it comes to antifreeze.

This is what Bitrex tastes like. TM Children’s Hospital of Pittsburgh

In 2012 antifreeze manufacturers in the US agreed to add a bittering agent, denatonium benzoate, to all products containing ethylene glycol (EG). Also known as Bitrex, denatonium benzoate is the bitterest substance we know of. It only takes a small taste to get you to make the Mr. Yuk face.

However, subsequent studies found the addition of denatonium benzoate makes no difference in the amount of antifreeze ingested either accidentally or intentionally, or in treatment given or medical outcomes.

How is that possible?

The studies don’t say why making antifreeze taste bad doesn’t make a difference in how much people drink, but there are possible explanations.

Accidental ingestions of antifreeze happen because it’s bright green, like a sweet drink might be, and sometimes it’s decanted into an inappropriate container, like a drink bottle. When someone mistakes antifreeze for a drink, it only takes one taste or swallow to realize their mistake anyway, so it isn’t surprising Bitrex wouldn’t change that.

And as for intentional ingestions, a bad taste may simply not be enough to discourage someone bent on self-destruction. Cats and dogs are able to taste the bitterness, but while cats may reject denatonium, there’s no evidence it turns dogs away.

What’s so bad about antifreeze?

Most antifreezes contain ethylene glycol (EG), which has a very low freezing point and a very high boiling point. Adding it to the water in a car’s radiator helps keep the water from turning to ice in the winter or to steam in the summer.

As awesome as EG is for your car, though, it’s hard on your body, and it only takes a very small ingestion to put you (or your child, or your pet) in the hospital. The problem isn’t so much with the EG itself as with the chemicals it breaks down to.

The first toxic metabolic product formed from EG is glycolic acid. Glycolic acid in small amounts is harmless; in fact, it occurs naturally in many fruits and vegetables. But large amounts circulating in the body can lead to metabolic acidosis, lowering the body’s pH to dangerous levels.

As the glycolic acid is further metabolized some of it is broken down to oxalic acid. Oxalic acid binds with calcium in the bloodstream and forms calcium oxalate crystals. When calcium gets bound up in crystals this way it never makes it to the muscles, including the heart, that require it for proper functioning, and the consequences can be severe. The crystals also build up and block blood flow to the kidneys, causing acute renal injury. As the kidneys fail, calcium oxalate crystals may begin to accumulate in other parts of the body such as the heart and joints.

How much is too much?

For humans, a potentially toxic dose of antifreeze that is 95% EG is estimated to be about 0.2 ml per kilogram of bodyweight. A lethal dose is estimated to be 1.5 ml per kilogram of body weight. For example:


  • Toxic @ 25 lbs = 11 kg x 0.2 ml = 2.2 ml, or less than half a teaspoon. A full swallow for a child is about a teaspoon.
  • Lethal @ 25 lbs = 11 kg x 1.5 ml = 16.5 ml, or a little more than a tablespoon; about 3 swallows for a child.


  • Toxic @ 150 lbs = 68 kg x 0.2 ml = 13.6 ml, less than a tablespoon. A full swallow for an adult is about a tablespoon.
  • Lethal @ 150 lbs = 68 kg x 1.5 ml = 102 ml, or less than half a cup.

The minimum lethal dose for cats is 1.4 mg/kg, and for dogs 4.4 mg/kg.


  • Lethal @ 9 lbs = 4 kg x 1.4 ml = 5.6 ml, a little over a teaspoon.


  • Lethal @ 20 lbs = 9 kg x 4.4 ml = 39.6 ml, about a sixth of a cup.

If you take an accidental taste of EG antifreeze and immediately spit it out, rinse your mouth and call poison control (800.222.1222) for advice.

But keep in mind: A full swallow of EG antifreeze requires prompt medical attention.

How is antifreeze poisoning treated?

We are able to drink and enjoy beverages containing ethanol, also known as ethyl alcohol, thanks to enzymes called alcohol dehydrogenases (ADH). There are different kinds of ADH and the mix and amount you have in your stomach and liver will vary according to your gender, age and ethnic makeup. It’s likely we and other creatures evolved with ADH because rotting fruit produces ethanol, and scavengers can’t always be choosers.

EG is also an alcohol, and ADH starts the process of breaking it down into its toxic by-products. Once those by-products are formed treatment is symptomatic: Sodium bicarbonate for acidosis, dialysis for renal failure. But if the ADH is prevented from acting on the EG in the first place, poisoning can be prevented.

Fortunately, as it happens, ADH would much rather partner with ethanol, and so ethanol itself makes a very effective antidote for EG poisoning. Maintaining a blood alcohol level of 100 to 150 mg/dl ties up enough ADH to keep EG from being metabolized. The most effective way to control the blood alcohol level is to infuse ethanol intravenously, but in an emergency it can be given by mouth.

Of course, there are downsides to keeping a patient drunk, especially if the patient is a pet, a child, or an adult who for other reasons should not indulge. A non-alcoholic antidote called fomepizole binds ADH without causing intoxication and is preferred over ethanol.

The less toxic alternative

EG antifreeze is still popular and widely available, but it’s also possible to buy antifreeze made from propylene glycol (PG). PG is generally nontoxic and is used in a very large variety of medications, foods and cosmetics. It can be mildly intoxicating in unreasonably large amounts but so far PG abuse doesn’t seem to be a thing.

PG antifreeze will be labeled “alternative,” “safer,” “low tox” or just “PG.” If it’s in a transparent container it will be pink. It may have a small amount of sodium nitrite added to help prevent corrosion.


Taste changes don’t stop poisonings
The impact of bittering agents on pediatric ingestions of antifreeze
The impact of bittering agents on suicidal ingestions of antifreeze
Overview of ethylene glycol toxicity (veterinary)

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