The question of whether cranberries, in some form, have value in treating or preventing urinary tract infections (UTIs) is a pretty old one. Mark Crislip at Science-Based Medicine has written a nice summary of the topic, and he has found over 100 references dating back to 1962. Like most herbal remedies, it has traditionally been thought helpful for a wide variety of unrelated disorders, but it is now pretty firmly established in most people’s minds as useful for UTIs.

Unfortunately, as usual the subject is more complicated than is generally realized. The theoretical justification for using cranberry to treat UTIs used to be that it acidified urine and made it less hospitable for bacteria, however that is no longer believed to be true. The current theory is that chemicals called proanthocyanidins interfere with the attachment of bacteria to the bladder wall, making it easier for the body to eliminate these bacteria and harder for infections to get started.

This is certainly a plausible mechanism established  by in vitro studies. The trouble is that the proanthocyanidins inhibit attachment only for E.coli with little hairs called fimbriae on them. There are many other bacteria that can cause UTIs, and there isn’t yet any evidence that proanthocyanidins affect these. And in humans fewer than 20% of E.coli in bladder infections have fimbriae, so theoretically, these chemicals should be only be useful in preventing recurrent infection in a small minority of cases. (Interestingly, the vast majority of E.coli from kidney infections are fimbriated, so cranberry could possibly be more useful in these cases). There is also the problem that no one has actually proven that oral cranberry leads to proanthocyanidins getting into the urine, or being biologically active when they get there.

As Dr. Crislip points out, though, the theoretical mechanisms are not so important if the remedy doesn’t actually work in clinical trials. So does it? Well, there is still no consensus, since some trials show and effect and others don’t. The best that can be said as of now is that cranberry probably isn’t useful for treating UTIS and it may or may not be useful for preventing them.

Despite this uncertainty, the popular belief that cranberry products are useful for urinary tract infections in humans makes it inevitable that such products will be marketed to pet owners for UTIs in dogs and cats. As in humans, many UTIs are caused by bacteria other than E.coli, and I am not aware of any research on the proportion of fimbriated E.coli in canine and feline UTIs, so the theoretical rationale for this remedy is even weaker than in humans. But a quick Google search shows plenty of veterinary versions on the market anyway, often with pretty confident claims.

I recently came across some marketing materials for one of these, Crananidin from Nutramax. They are careful to avoid any treatment or prevention claims, since that would violate the Dietary Supplement Health and Education Act (DSHEA). However, they try pretty hard to suggest a benefit and even superiority over their competitors despite the absence of any clinical trial evidence.

The Nutramax literature has a nifty little graph of bioactivity in the dog purporting to show that “by 7 days the average bioactivity is over 78% at inhibiting E.coli.” They cite two articles to support this statement. One is an NMR study of the molecular structure of proanthocyanidin, and the only bioactivity data is from mixing fimbriated E.coli with human red blood cells and some cell-surface-receptor coated plastic beads in vitro (interestingly, this study was funded by Ocean Spray). There is no testing or discussion of clinical effects, and no data concerning dog urine. There really seems no way to interpret this citation other than being deliberately misleading.

The other reference is “Data on file, Nutramax Laboratories,” so I presume it is an unpublished in-house experiment. Unpublished data from a company selling a product that “proves” the product works, and is better than the competition, ought to be viewed somewhat skeptically, needless to say.

The marketing literature also has a little chart showing their product “passing” a test of bioactivity and all the competing products failing it. The references for this are the same, and since the published article has nothing to do with this issue, apparently the only evidence for this claim is unpublished in-house data from Nutramax. I’m not aware of any published clinical trials investigating this or any other cranberry product for use in UTIs in dogs or cats.

There also isn’t any evidence concerning the safety of cranberry products in dogs and cats. In humans, one concern is that cranberry juice has a lot of salicylic acid, so people with aspirin allergies or on anti-coagulant medications aren’t supposed to take a lot of it. But those are pretty rare issues in veterinary medicine. And some studies have shown it increases oxalate in the urine by up to 43%, so I wouldn’t recommend it for patients with a history of oxalate urinary tract stones (even though, again, this data is for people, and there are no studies I can find in dogs or cats).

Bottom Line
There is weak theoretical justification for using cranberry products for UTIs, though none of the supporting preclinical evidence involves dogs or cats. There is conflicting clinical trial evidence in humans, and no clinical studies in dogs and cats. There are weak theoretical safety concerns. And, of course, there is abundant marketing making bold statements unsupported by the little evidence that exists. You pays your money and you takes your chances. Fortunately (for Nutramax, if not for our pets), anecdotes claiming a benefit are easy to find, so there should be little trouble selling the products even without convincing evidence of safety or efficacy.

Last year I wrote a review of a dubious herbal combination product called Protandim. At that time, my bottom line conclusion was:

Bottom Line
The underlying theory used to promote this product, that anti-inflammatory and anti-oxidant effects are always safe and beneficial, is highly doubtful. There is only weak in vitro and animal model research to indicate that the ingredients in Protandim, or the combination product, have potentially useful effects on cells or biochemical markers. There is absolutely no clinical trial evidence to indicate Protandim has any of the claimed benefits in humans or animals. While the absence of evidence is not proof the product is unsafe or ineffective, it is absolutely a reason to be skeptical of wild claims of miraculous benefits. At best, using this product is simply rolling the dice and hoping for the best. That seldom works out for gamblers in Vegas, and it is not an appropriate approach to healthcare except in the most dire of circumstances.

Dr. Harriett Hall at the Science-Based Medicine Blog has recently provided an update on this product and a recent clinical study investigating it. The study was bizarre and it is amazing any ethics committee would approve it. It is also not prominently featured on the Protanidim web site, no doubt because no effect was seen. Here are a couple of highlights from Dr. Hall’s summary:

To recap their chain of reasoning: alcoholics might develop lung disease, that lung disease might be correlated with abnormal epithelial permeability, protein levels measured by bronchoalveolar lavage (BAL) might be a valid measure of permeability, permeability might be affected by underlying oxidative stress, and Protandim might reduce oxidative stress by stimulating the body to produce its own antioxidants. Do they perhaps think that lots of “mights” add up to a “mighty” argument?

The second listed author, Joe McCord, has a vested interest: he is an officer of the LifeVantage company, the manufacturer of Protandim. They explain that Protandim is “a nutraceutical with a lengthy history of use in homeopathic, Ayurvedic, and traditional Chinese medicine.” An interesting statement, since Protandim was invented only a few years ago by a person with no medical background and it was patented in 2007. Doubly interesting since it belies the common myth that natural medicines are not profitable because they can’t be patented.

They assessed alveolar epithelial permeability by measuring the total protein in bronchoalveolar washings. Total protein levels did not change in either experimental group. They also found no change in oxidative stress indices, epithelial growth factor, fibroblast growth factor, interleukin-1?, interleukin-10, liver function tests, or other blood chemistry tests. The one finding that was statistically significant was a significant decrease in plasma thiobarbituric acid reactive substances (TBARS), a marker of lipid peroxidation — but that was only in the placebo group!

In short, Protandim was significantly (p<0.01) worse than placebo. No wonder they’re not bragging about this study!

Big Pharma gets a lot of criticism, but aren’t Big Supplement and Big Multi-Level Marketing every bit as guilty of self-interest, distortions, and profit motives? At least Big Pharma can’t make its big bucks without first demonstrating effectiveness and safety to the FDA with clinical trials.

Does Protandim provide any real benefit to its customers? I don’t know, and they can’t hope to know unless they do proper clinical studies.

Knowing that I have an interest in investigating the evidence behind claims for veterinary healthcare products, clients and colleagues sometimes pass along materials concerning veterinary supplements, herbal remedies, and other similar products and ask my opinion. Since there are hundreds, if not thousands of products marketed to pet owners to preserve or restore their pets’ health, I can only look into a few. However, the more of these I investigate, the more clearly I see the patterns of disregard for science and manipulation of the consumer that they have in common.

The latest in this category is a collection of products from a company called Nzymes.com. The website and pamphlet for this company exhibits nearly all of the warning signs of quackery. The company systematically tries to frighten the consumer by suggesting that pets cannot be healthy without their product and that the food and healthcare they are currently getting is inadequate.

Give Your Pet a Fighting Chance

If you are feeding your pet one of today’s popular processed pet foods, then chances are, your pet’s body is depleted of the primary enzyme precursors nature provides abundantly in all living foods.

The fact that we continue to feed our pets such enzyme-less food over an entire lifetime may contribute to the growing list of animal health problems we witness today including; osteoarthritis, inflammation, joint pain, hip dysplasia, pano, OCD, HOD, shedding, hair loss, dry skin, itchy skin, digestive disorders, gastritis, pet food allergies, epilepsy, fatigue, hot spots, and many other stress related symptoms contributed to by a weakened immune system.

The whole “living enzyme” argument is complete nonsense, and there is no evidence for the suggestion that commercial diets are nutritionally deficient or responsible for this long, redundant list of random symptoms and disorders. Some of these problems may be related to nutrition, but that has nothing to do with the claim made here, which is baseless.

But the pseudoscientific nonsense doesn’t stop there. The web site also blames pet food, vaccines, and medications for a variety of ailments, again without paying any attention to the real, and complicated, risks and benefits of these interventions. Classic quack nonsense like claims about the Pottenger cat “study,” about boosting the immune system, about mysterious “toxins” as a cause of unrelated diseases,  and about Candida yeast infections as a common cause of many health problems are all over the company web site.

So, what are they selling with all this fear? Apparently, miraculous panaceas with uncounted benefits and absolutely no risks! Since they aren’t allowed to claim they can actually prevent or treat any disease without having evidence to support it (though they effectively do, despite the Quack Miranda Warning here and there), they promise to “support”

Healthy Joint function, Healthy Muscle Function, Healthy Skin and Coat, Healthy Nervous System, Healthy Immune System, Healthy Circulatory System, Healthy Endocrine System, Healthy Lymphatic System, Healthy Digestive System, Healthy Urinary Function, Healthy reproductive Function, Healthy respiratory System, Healthy organ Function, General Overall Wellbeing

I like how they throw in “Healthy Organ Function” and “General Overall Wellbeing” just to cover any possible body part they might not have thought of. So if you’re afraid the imaginary causes of illness they mention have caused your pets’ problem, or might cause something bad someday, you can take comfort from knowing they this product can treat or prevent absolutely everything (except when it can’t, in which case it’s because of the food, the water, the medications, or anything else except the lack of benefit of their product). 

What, exactly, are the miracle elixirs offered by Nzymes.com?

Ox-E drops
This consists of 5% sodium chlorite, a chemical related to bleach. Properly diluted, this chemical is a safe disinfectant, killing infectious organisms through oxidation. With a pH of 13, if not diluted the chemical can cause burns, especially to the eyes and mucous membranes. Accidental overdose can be fatal.

The company advertises this as helping in “the removal of potentially dangerous free radicals and toxins,” and claims that is boosts the immune system, supports digestion, and enhances “performance.”  Impressive claims for a potentially toxic disinfectant that is actually an oxidant rather than an anti-oxidant.

As the accompanying quack Miranda warning attests, and a simple literature search confirms, there is absolutely no evidence for any of these claims. Plenty of testimonials are offered, of course, which is always the evidence of choice for products that are based on pseudoscience and have never been tested in any reliable way.

Antioxidant Treats
The antioxidant hype is a common marketing ploy for supplements because it’s vague, and there is enough suggestive preclinical research to suggest the general idea is plausible. Unfortunately, there are few clinical trials which show significant real benefits from particular anti-oxidants in particular conditions, and the evidence is growing that some such agents, such as Vitamin E, can actually increase the risk of disease.

The specific ingredients include Vitamin A, Vitamin C, Vitamin E, and a proprietary freeze-dried sprouted soybean meal claimed to contain:

The amount of the vitamins in the supplement are far in excess of what is recommended to prevent deficiency.

Vitamin A- 1000IU (recommended daily dose 50IU/kg, safe upper limit 2,099IU)
Vitamin C- 30mg (recommended daily dose 0, dogs and cats make their own)
Vitamin E- 5IU (recommended daily dose 1mg/kg)

These amounts are probably not high enough to cause harm, but given that most pets are fed diets already supplemented with more than enough of each, the amounts in this product are unnecessary as nutrients. The use of excess amounts of these vitamins as medicines to prevent or treat disease, is not proven, and has often turned out to do more harm than good when tried in humans.

As for the sprouted soybean meal, there is no scientific evidence to suggest health benefits from this either. The company sites a variety of epidemiological studies in humans indicating an association between eating tofu or other soybean food products and lower cholesterol levels, rates of some cancers, and a few other health problems. (They do not, of course, refer to any of the research in humans showing lack of benefit or potential risks from soy supplement products). All of this, unfortunately, is entirely irrelevant to whether or not this particular soy-based product has any benefits for dogs and cats.

The amino acids, vitamins, and minerals listed are all provided in adequate amounts in good quality commercial pet foods. The enzymes are of no benefit, particularly when taken orally since they themselves are destroyed by normal digestion. And none of the phytochemicals have yet been demonstrated to have any health benefits in dogs and cats. So while it is unlikely to be harmful, to is an expensive way to get a few nutrients your pet probably already has enough of and some chemicals that may or may not have any health effects, positive or negative. 

Black Leaf Tincture
This is an herbal product containing black walnut extract, olive leaf extract, and cayenne in 75% alcohol(!). The usual vague and unscientific claims are offered about supporting the immune system, the circulatory system, the digestive system, and so on.

Black Walnut- There is insufficient evidence to support any of the claimed health benefits despite traditional use for a wide range of unrelated problems. There is some concern about possible toxicity, from the walnut itself and from possible fungal contaminates.

Olive Leaf- The evidence in humans suggests some possible beneficial effects on blood pressure and cholesterol levels, but it is weak and not conclusive. There is no eveidence on the possible effects in dogs and cats.

Cayenne- There is a fairly large amount of preclinical research suggesting possible benefits in humans, but little in the way of clinical trial evidence, and nothing in dogs and cats. 

Probiotic
I’ve written extensively about probiotics, and this is an area in which I think some real benefits are possible. Unfortunately, we have yet to develop an adequate understanding of the normal gut ecology to be able to influence it in significant ways, and the evidence for real clinical benefits from specific products varies from weak to non-existent. Nzymes.com does nothing to change this. Their product contains a variety of typical probiotic bugs, and there have been no clinical trials to show that the specific combination has any value. The product was tested, however, in a study looking at quality and label accuracy for veterinary probiotics. It was found to contain only 2.7% of the number of bacteria claimed on the label, suggesting even the ingredient claims made for this product may be questionable, much less the claims of health benefits. 

“A Veterinary Study”
The company does claim to have one rather large veterinary clinical study from 1989 showing that dogs with musculoskeletal pain benefit from its sprouted soybean product. The study was never apparently published, and the information provided on the web site does not make it possible to evaluate it extensively. Six unnamed veterinarians apparently diagnosed dogs with “musculoskeletal inflammation” based on their own exams and the opinions of owners. They gave the supplement to 387 dogs, and 340 of them were reported as improved in one of more of these measures: energy, alertness, stamina, appetite, and accelerated healing. Most cases improved within the first week.

This is almost a cartoon caricature of what a scientific study shouldn’t be. No randomization, no placebo control group, no standardized diagnostic evaluation, no objective diagnostic evaluation (all subjective), no clearly defined diagnosis, no blinding, no record of other conditions or treatments used, and no predetermined or even halfway consistent criteria for response. Any high school science class ought to be able to put together a better “study.” If this is the best the company has been able to do in over 20 years, there is absolutely no reason to believe they have any interest in the scientific validity of their marketing claims. 

Bottom Line
These products are being marketed with an impressive number of the myths and warning signs of snake oil and pseudoscience. The theories offered for why these remedies should help your pet range from complete nonsense to vague unproven hypotheses. There is no scientific evidence to indicate any specific benefit from any of these products for any particular condition in dogs and cats. All the testimonials in the world can’t prove any of the company’s claims to be true, nor can they guarantee that the products cannot hurt your pets. Just as there is little evidence regarding the claimed benefits of these products, there is little to demonstrate that they are safe.

The popularity of herbal remedies rests, in large part, on the perceptions of these substances as “natural,” a vague, nearly meaningless term often mistakenly understood to mean “safe.” The idea that eating parts of plants, singly or in combination, can have significant health benefits with little to no risk is one of the irrational cornerstones of alternative medicine. On the other hand, the idea that plants contain compounds which can have both beneficial and adverse health effects is a well-established and generally accepted fact. Herbal remedies very likely do have health benefits, we simply rarely have the data to identify these or the associated risks with enough certainty to justify claims made for them or clinical use of them.

Despite this, such remedies are not infrequently used by patients, often without the knowledge or guidance of healthcare professionals. Exactly how popular herbals are is unclear, but individual surveys suggest a small but significant number of patients use them. I recently ran across one such study, which illustrates the use of herbal remedies by human HIV patients and also sheds some light on the attitudes of such patients and on the potential risks of this behavior.

Vazquez Hernandez, M. Hurtado Gmez, MF. Blanco, JR. The influence of alternative medicine in highly active antiretroviral treatment. Farmacia Hospitalaria 2009;33(1):31-6.

Highly active antiretroviral treatment (HAART) is an approach which significantly reduces HIV morbidity and mortality and improves the quality and length of patient’s lives. While not a cure or devoid of side effects, it is a highly effective treatment that has had a tremendously positive impact on the well-being of people infected with HIV. As with most incurable conditions, however, there is a subpopulation of patients who are interested in alternative therapies to replace or augment conventional care. This study found 16.6% of the HIV patients surveyed used 1 or more presumably medicinal plants.

37.5% of these people thought of these plants as a form of medication, which is the appropriate perspective to take on herbal remedies, apart from the lack of evidence to document safety and efficacy for many of them. However, another 37.5% of the patients did not know medicinal plants could have any side effects, and none of the patients realized that these agents could interfere with the HAART that was so vital to their health. 62.5% of the patients did not know what the herbal remedy they were taking was, could not say what it was for, and were taking it on the advice of someone who was not a healthcare professional.

A variety of herbal agents were used, with grapefruit, milk thistle, and Echinacea being the most common. Though information about safety and possible interactions with pharmaceuticals is extremely limited for most herbal products (no literature was found for 54% of the agents used), some published evidence of negative effects of HAART was seen for 46% of the agents reported, including the three most common ones. The authors concluded:

Patients undergoing HAART regularly use medicinal plants and this often occurs without the knowledge of the doctor or pharmacist. There is evidence that herbal preparations can cause pharmacokinetic and pharmacodynamic interactions that represent a potential risk in patients undergoing HAART…

The population in general and the patients perceive these substances as healthy. The patients are not aware of the adverse effects that these can sometimes produce and that they can even cause HAART to fail. The reasons given for the consumption of medicinal plants is that the patients believe that these increase the efficacy of their treatment, improve their quality of life, reduce the adverse effects of HAART and give them a feeling of control.

This is a summary which probably applies equally well to many of groups of patients. Herbal remedies with significant but poorly understood physiologic effects can impact, both positively and negatively, the health of people who take them, but most people know little about what they are taking or why, do not understand that the benefits are unclear and that there are possible risks, and most rely on the advice of people other than their primary healthcare team. If herbal remedies are to find a place as effective medicines, we need to develop the research base to understand their effects and we need to educate patients and healthcare professionals about the potential risks and benefits and interactions with other therapies. This, of course, requires debunking the fallacy that such products are inherently safe because they are “natural.”

One of the most popular plant products touted for medicinal use in pets is garlic Allium sativum. A recent newsletter by Dr. Deva Khalsa, a popular alternative veterinarian, makes some typical claims:

Garlic is a miracle herb!

Garlic (Allium sativum) has been valued for thousands of years for medicinal purposes.

reported adverse affects from garlic add up to a total non-event over the past 22 years….This proves beyond the shadow of a doubt that the risk of using garlic is so infintessimally low that it’s simply statistically insignificant. What is significant is all the positive research delineating the medicinal powers of garlic.

a natural antibioitic

it’s antifungal, antiviral and antibacterial effects can contribute to the healing process.

Garlic increases general immune activity

Uncooked garlic helps to lower blood triglycerides and choleterol making it useful for certain breeds (Schnauzers and Beagles) that are predisposed to this problem.

Compounds in garlic act as antioxidants and help flush toxins out.

garlic has been fed to dogs in order to help prevent flea infestation.

A host of studies provide evidence that the allicin in garlic works to inhibit cancer formation.

Since these pretty fairly represent the claims made for garlic, I will address each in turn.

1. Garlic is a miracle herb-
Well, miracle is a pretty tough word to justify when applied to any medical therapy, all of which come with pros and cons. I’d call this a warning sign!

2. Garlic has been used medicinally for thousands of years.
True, but irrelevant to whether or not it works. The traditional use of plants as medicines has a poor record of predicting uses that are actually proven valid by controlled scientific testing. Here are some of the traditional uses record for garlic (from Wynn SG. Fougere BJ. (2007). Veterinary Herbal Medicine St. Louis: Mosby Elsevier.)

Traditionally, garlic has been used in humans [or animals] for abnormal growths, bronchitis, pneumonia, digestive problems, intestinal infection, tuberculosis, dysentery, earache and ear infection, vascular disorders…influenza…relieve toxicities, and kill parasites…treatment of a cow that was unable to rise after calving…coccidiosis in poultry…breast tumors on dogs (topically), for distemper, for jaundice, for rheumatism, and for thyroid complaints and worms…for fungal infection and swelling of the tongue, oral blisters and wounds…contagious abortion, tetanus, milky diarrhea, abdominal pain, asthma, polyuria, sores, compound fractures, epilepsy and swelling of the kidneys, gangrene of the lung…

When something is used to treat such a wide variety of apparently unrelated medical conditions, either it is a miracle or it is an example of how easily people can be fooled into thinking a useless therapy is helping. A truly miraculous therapy shouldn’t have any trouble proving itself in scientific testing, so when the evidence is lacking despite centuries of use and decades of research, the most likely explanation is human fallibility rather than miracle cure.

3. Risk of using garlic is negligible.
Mostly true. A number of in vitro and lab animal studies have shown the potential for garlic to cause anemia and other problems. Studies looking at garlic as a potential antimicrobial in swine feed found the pigs ate less and gained less weight (and also had and “objectionable” taste, for those carnivores among you). However, the amount of garlic which must be fed to cause clinical illness in dogs is probably much larger than is typically used. Cats are much more sensitive, but they are also less likely to accept garlic.

There are a couple of important caveats here, though. For one thing, the in vitro and lab animal studies showing potential dangers of garlic, which Dr. Deva and other proponents of garlic dismiss as not relevant to actual use, are exactly the same kinds of studies which show potential benefits and which they constantly cite to justify actual use of garlic. This is a classic case of confirmation bias in which people accept as valid evidence which supports their position but reject evidence which contradicts it.

The other factor is that there are case reports of individual dogs who experienced anemia, high blood pressure, and other serious adverse effects from consuming relatively small amounts of garlic (e.g. 1, 2). It is often the case with pharmaceuticals, which appear safe in relatively small test populations of a few thousand people, less common sensitivities in some individuals appear when they are given to much larger numbers of patients. This is part of the business of balancing the risks and benefits of any treatment. So while the risks of garlic appear to be low for most dogs, it is not appropriate to assume they are inconsequential, especially when evidence for benefits is so poor (as we will see).

4. Garlic has antibiotic, antifungal, and anti-parasitic properties.
Maybe. The basis of this claim, apart from low-reliability evidence such as anecdote and opinion, is in in vitro and animal model studies. Chemicals from garlic do have effects on bacteria, fungi, and parasitic organisms in the laboratory. This only suggests that these chemicals might have similar effects in the real world. It doesn’t prove anything. What an isolated chemical does in a petri dish is not necessarily what feeding garlic will do in a living animal. And as I often remind people, bleach has antibiotic, antifungal, and anti-parasitic properties in the lab, but I wouldn’t recommend it as a dietary supplement!

The research in real animals is mixed. Garlic has failed to show benefit in at least as many studies as it has shown some effects, so the balance of the evidence is unclear. And the published research is almost all in agricultural animals, not companion animals.

5. Garlic “boosts” the immune system.
Nonsense. The notion of a general immune stimulant which has clinically beneficial effects and no side effects is a fantasy that ignores the incredible complexity of the immune system and how it interacts with all the potential threats it is exposed to. This empty bit of marketing is discussed, and demolished, in detail in this article.

6. Garlic lowers triglycerides and cholesterol.
Probably not. A 2009 review of the research in humans found that “the available evidence from randomized controlled trial does not demonstrate any beneficial effects of garlic on serum cholesterol.” The point is largely moot since blood lipids are almost never a meaningful health issue in companion animal species. It is true, as Dr. Deva suggests, that it is an uncommon problem in certain breeds. However, I would note that both of the dogs in the case reports I mentioned before who suffered harm from eating garlic were Schnauzers, the same breed that most often exhibits this otherwise rare problem. So I’d be very careful about suggesting garlic as a remedy for this issue in this breed given the lack of evidence for a benefit and the presence of evidence for possible risk.

7. Garlic is an anti-oxidant and helps remove “toxins”
A hypothetical treatment for a hypothetical problem. First off, the subject of oxidation and anti-oxidants is about as complex as the subject of immune system activation, and there is growing evidence that anti-oxidant therapies do little good and some harm (e.g. 3, 4, 5). So while garlic compounds show some antioxidant properties in the lab, they also show the ability to cause oxidative damage (that’s where the anemia comes from), and there is zero evidence in real cats and dogs for any benefit from garlic as an anti-oxidant.

Secondly, the mysterious “toxins” so often mentioned as a target for health promoting therapies are a classic sign of snake oil marketing. Without information about specific toxins, evidence for the harm they do, information about how they are processed and eliminated by the body, and evidence concerning how garlic can aid in this process, this claim is totally meaningless. And, not surprisingly, none of the information or evidence is offered for garlic.

8. Garlic is an effective flea control method.
Doubtful. There are, of course, plenty of anecdotes from people saying that garlic drove the fleas away from their pets like magic. There are just as many that say garlic didn’t help at all. There is absolutely no research evidence showing garlic supplements to be an effective form of flea control. It is often given with Brewer’s yeast, which has been shown to be ineffective as a flea repellant. So for all the confidence with which this claim is made, it is simply made up.

9. Garlic is useful in prevention or treatment of cancer.
Maybe. There is low to medium level evidence in humans that eating garlic may reduce the risk of some kinds of cancer. The American Cancer Society concludes

there is not enough evidence at this time to support eating large amounts of garlic or taking garlic supplements for cancer prevention. Garlic may have the potential to interfere with anesthesia or other medicines. It is reasonable to include garlic as part of a balanced diet, unless one has a particular health problem or is taking medication that has been shown to be adversely affected by garlic.

Other research summaries show a mix of possible benefits and risks, including bleeding and interference with the action of a number of medicine. So like anything with the potential for benefit, there is the potential for harm.

And, as usual, none of this research has been done in companion animal species. So while extrapolation from research in humans is often necessary, it is also a great way to draw the wrong conclusions. Such research strongly suggests which ideas may be worth pursuing and which may not, but it certainly doesn’t provide a confident, reliable answer about what to do for our pets.

Bottom Line
In vitro and lab animal research suggests a number of potential uses for garlic. The same level of research suggests some potential danger to garlic use in dogs and cats. There is almost no clinical research to substantiate any of the claims made for garlic use in pets. Traditional use suggests almost every pant is a cure-all, and the majority of such claims have yet to pass the test of scientific study. So at this point, hysterical claims of garlic as a “miracle food” are totally unjustified. The potential benefits deserve to be investigated, but they are mostly theoretical and unproven. The risks are probably low overall, but some individuals have been harmed by eating garlic, and we are currently unable to predict accurately which patients will be adversely affected.