Skeptoid PodcastSkeptoid on Facebook   Skeptoid on Twitter   Skeptoid on Spotify   iTunes   Google Play

Members Portal

Support Us Store


Get a Free Book



Homeopathic and Natural Dog Supplements - Garlic

by Eric Hall

April 13, 2013

Share Tweet Reddit

Donate When I started back writing for Skeptoid on a regular basis, I asked on my social media accounts what people would like to see me cover. One that had a few votes was Homeopathic treatments for dogs. As I have started researching these things, I was surprised (but perhaps should not have been) at how much of this woo is out there. It also follows the template of woo sold to humans. Because of the amount of misinformation out there, I will periodically write about small pieces of it to provide quick reference to those who are reading!

For the first topic, we start with garlic for dogs.

The Science

What makes garlic potentially harmful to dogs is thethiosulphate contained in it. This is the same compound that also makes onions, chives, and related plants harmful to dogs. Dogs do not have the enzymes to break down thethiosulphate in digestion, so it is able to reach the blood andleads to a destruction of red blood cells - a condition known asHeinx Factor anemia. That would seem to be enough to keep garlic away from dogs.

However, as with many things, it is about dose. It was difficult to find exact numbers, but it would appear garlic contains anywhere from 5-10 times less thiosulphate than anequivalentamount of onion. Many of the websites promoting garlic for dogs say it is "non-existent," which is not true. The amount is less, but it is not zero. Because foods that are close to their natural state like fruits and vegetables have some variation in the constituent nutrients and other chemicals, there isn't an exactcomparisonto be made, but it seemssufficientto say the amount ofthiosulphate in garlic is quite a bit less than an onion.

The sole piece of research directly diet to dogs and garlic comes from a 2000 study in theAmerican Journal of Veterinary Research. The study fed garlic to 4 dogs, with a second group of 4 dogs as control. The dose was fairly large. An extract was given, which wasequivalentto about 5 grams of garlic per kilogram of mass for the dog. 5 grams is a little less than one clove. Studies done on onions show toxicity in dogs is about 10 grams per kilogram. So if garlic contains less of the compound responsible for toxicity and is given in a dose much lower than what causes toxicity in a similar circumstance (onions), then it would seem there shouldn't be a toxic effect.

It turns out dogs did not show toxicity signs in this study. However, the blood tests reveal a different story. The abstract states:
Compared with initial values, erythrocyte count, Hct, and hemoglobin concentration decreased to a minimum value on days 9 to 11 in dogs given garlic extract. Heinz body formation, an increase in erythrocyte- reduced glutathione concentration, and eccentrocytes were also detected in these dogs. However, no dog developed hemolytic anemia.
So the dogs did show signs of damage to their blood, but did not have outward symptoms of the disease.

Some other negative effects of garlic toxicity include:vomiting, diarrhea, anemia, tachycardia, weakness, liver damage, allergic reactions, asthmatic attacks, contact dermatitis, and gastrointestinal damage. Although often cited, the dose required for these effects was not listed in the resources I could find. It would seem these symptoms were based on seeing animals with garlic toxicity, and not in a controlled study. Therefore, the dose required for toxicity is unknown.

The Claims

Some of the websites promoting the use of garlic include.
  • Garlic has been known used for hundreds of years for its health benefits

  • Garlic contains germanium - an anti-cancer agent

  • Garlic helps to regulate blood pressure

  • Garlic helps strengthen the body's defences against allergies

  • Garlic helps regulate blood sugar levels;

  • Garlic is high in vitamins, minerals and nutrients:
    • Calcium, Potassium, Zinc

    • Protein

    • Vitamin A, B, B2, C

  • Garlic is an aid to fighting and treating:
    • Diabetes

    • Liver, heart and kidney disease

  • Garlic is a natural antibiotic and won’t affect the good bacteria in the gut which are needed for digestion and immune health

  • Garlic is antifungal

  • Garlic is antiviral

  • Garlic boosts the immune system

  • Garlic makes dogs less desirable to fleas

  • Garlic is antiparasitic

  • Garlic is a natural flea repellent and de-wormer

Are the claims true?

Some of the claims can be dismissed fairly easily. For example, the idea of boosting the immune system is nonsense at any level. It really has little meaning. If the immune system needs "boosting" due to a disease or some other condition, there are specific treatments for that. Eating a certain food or taking a certain vitamin by itself will not change that. In fact, the claim of helping to fight allergies goes in direct opposition to the "boosting" claim. If the immune system is "boosted," it will much more readily perform an immune response. These are pretty standard claims made by psuedoscientific sites, and can be dismissed as mostly nonsense.

One of my favorite claims is: "Garlic is a natural antibiotic and won’t affect the good bacteria in the gut which are needed for digestion and immune health." As anyone who has taken an antibiotic for an infection can tell you, antibiotics do have an effect on gut bacteria. I am sure a claim could be made that our gut bacteria have evolved resistance to the antibacterial properties, but I wasn't able to find any actual research on that. It seems pretty unlikely that garlic could perfectly target "bad bacteria" while not hurting "good bacteria."

Similarly, most of the other claims have very little research to back them up. The idea of getting nutrients from garlic as a benefit seem to be reasonable, but in the amounts suggested it would be a minimal addition to their main food supply. The idea of garlic being used for hundreds of years is a common logical fallacy. Bleeding people was also a common practice a few hundred years ago - that doesn't make it good.

The claim of antifungal does seem to have some validity. However, the studies that show promise are in humans, and the compoundsextractedfrom garlic are applied topically, not ingested. The fighting flea idea also has plausibility, as studies in humans have shown a reduction in tick bites in people who take high doses of garlic, but the effect on other bugs or what the minimum dose needed would be has not yet been studied.

Claims of other nutrients such as selenium make sense in a broad perspective. Like humans who need a balanced diet to ensure wereceivethese tiny amounts of various minerals, dogs need them as well. However, garlic is not the only source for selenium (and vitamins) - and a good, high-quality dog food can provide the same benefit.

What's the Harm?

The "natural" pet care websites mostly suggest 1/2 a clove of garlic for every 10 lbs of dog per day. One other dose that some "holistic" vets recommend is 1/4 per 10 kg (about 22 lbs) per day. Based on the one study, these should be far below a dose which would show signs of toxicity. Due to lower levels ofthiosulphate in garlic than onions, reports on onion toxicity, and the garlic study, it would seem these levels of garlic won't kill an otherwise healthy dog.

Websites will give you mixed messages. One message board I found was full of anecdotes with a wide degree of outcomes. Some of the bad stories include:
"Garlic IS deadly for dogs. My poor sheltie just died a few days ago from eating 3.5 ounces of dried garlic he got into. He was totally healthy and fine before that. He was throwing up, became lathargic and with 8 hours was DEAD. I wish I would have know it is toxic to dogs, I would have taken him to the vet and they could have used charcoal on him, blood transfusion to replace the bursting blood cells and/or oxygen treatment. It causes a certain type of anemia and eventually kidney failure."

"...never use garlic on a pregnant dog- it will make the milk toxic for the puppys. I learned that the hard way."
In the "positive" stories, there are outcomes listed such as not needing to vaccinate, fighting cancer, avoiding "chemically laden" food, curingarthritis, etc. In either case, these are anecdotes, and I don't put much weight in what they add to the information. But, it is interesting that these sites often tout the "safety" over "traditional" care, yet "natural" care seems to have as many reports of adverse events as "traditional" care.


It would seem that even small amounts of garlic does cause a physiological effect in dogs. It would appear that the doses recommended by these "natural" sites won't cause any long-term damage despite these effects on the blood in dogs. However, there is no appreciable benefit to garlic supplementation either. From a risk/benefit perspective, I wouldn't supplement dogs with garlic because, although the risk is small, outweighs any nutritional benefit. Any benefits can also be derived from other sources with less risk.

I say, save the garlic for a better use - like your own pasta sauce and fresh garlic bread!

by Eric Hall

Share Tweet Reddit

@Skeptoid Media, a 501(c)(3) nonprofit








Want more great stuff like this?

Let us email you a link to each week's new episode. Cancel at any time: