Potentially Unsafe Herbs for Pets

Herbs are now widely used as an alternative or complementary treatment option for pets. Although most herbs are safe for use in pets, not ALL are safe. This page is about some unsafe herbs that have to be used with care (for example, garlic, comfrey, tea tree oil) or are not suitable for use at all in treating our pets (e.g. pennyroyal, wormwood).

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Some people mistakenly believe that because herbs are "natural", as such they are "safe". The bad news is, that is not true. Like any other therapeutical substances, certain herbs can cause side effects. Others can even be toxic or even lethal to some animals when used inappropriately.

Sometimes an herb can cause side effects by itself; other times the use of an herb might interfere with the actions of a conventional drug or increase the chance of side effects when used in conjunction with certain drugs.

However, having said that, herbs are generally less likely to cause the type of nasty side effects caused by conventional medications.

The bottom line is, when you are unsure whether a certain herb is safe for your pet, consult a holistic vet first - especially if your pet is on conventional medications, or is already weakened by certain ailment(s).

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Unsafe Herbs for Pets

The following unsafe herbs are potentially dangerous for use in animals and care should be exercised when using them:

Pennyroyal

While this herb (and its essential oil) is an effective insecticide, it is toxic to dogs and cats at high doses. In particular, it should NEVER be used in pets with existing kidney disease. The essential oil of pennyroyal is extremely concentrated and, to be on the safe side, should not be used on dogs and cats, especially if they are pregnant.

Tea Tree oil

Undiluted tea tree essential oil is VERY toxic to cats and small dogs. (In fact, cats are extremely sensitive to essential oils and it is better not to use essential oils on cats.)

For bigger dogs, use tea tree oil with care. Always dilute the essential oil (0.5-1%) in a carrier oil (e.g. olive or almond oil). Test a small patch of skin prior to use as some pets may be sensitive to the oil.

Comfrey

Comfrey contains small quantities of alkaloids that can cause liver damage or cancer if taken in large quantities or prolonged period of time. Therefore, if comfrey is to be used internally, use it for short periods and in moderation. Also, do not use comfrey in pregnant or lactating pets or those with pre-existing liver disease.

Since the alkaloid concentration is ten times higher in the root than the leaves, DO NOT use comfrey root internally. Comfrey dried leaves, on the other hand, contains very little alkaloids so use the dried leaves if needed.

White Willow Bark

White willow bark contains salicylates (same as in aspirin) which may be toxic to cats. Also, do not give this herb to your dog if he is taking NSAIDs (non-steroidal anti-inflammatory drugs).

Ma Huang (Ephedra)

This Chinese herb is most commonly prescribed for pets with asthma or respiratory problems. However, it can cause heart arrhythmias (irregular heartbeat) and high blood pressure in animals, and some reports also state that it may cause idiosyncratic reactions in cats. Use with great caution in all pets.

Wormwood

Wormwood is a traditional deworming herb. It is however too strong on pets, because it contains strong volatile oils, tannins, and bitter principles. If used excessively, it can irritate the liver and kidneys, and may even damage the nervous system in extreme cases. The dilemma with wormwood is, if used in small amounts, it is ineffective in deworming. If used in bigger doses, it may cause problems to our pets! Since there are other safer natural remedies for deworming, it is advisable that we use wormwood with extreme caution and only under strict holistic veterinarian advice.

Yucca

If used in large doses or over an extended period of time, yucca can irritate the stomach lining and intestinal mucosa, which may cause vomiting and bloating.

If used in small doses, yucca is safe. Therefore, avoid giving yucca to your pets more than 4-5 times per week, more than a month or two at a time, or during pregnancy.

Garlic

Garlic in large amounts can cause Heinz body anemia in dogs and cats. It is not advisable therefore to use garlic in pets with anemia. However, if fed in small amount, garlic is good for many uses, including the treatment of parasites such as fleas and worms, microbial infections, and in the treatment of cancer. One clove of garlic per 10 pounds of body weight for dogs (and 1/2 clove per cat) can usually be fed safely each day. Visit our page on Garlic for Dogs for more information on this herb.

Possible Side-Effects of Herbs on Pets

Different animals may react differently to the same herb. For example, certain herbs may cause slight allergic reaction in some pets, while other pets are unaffected.

Some possible side-effects are:

  • runny eyes and nose
  • sneezing
  • itching
  • swelling
  • diarrhea or vomiting

Interference with Conventional Medicines

Certain herbs are not unsafe herbs by themselves but, when used in conjunction with some conventional medicines, may interfere with the conventional drugs. Therefore, as a general rule, consult a holistic vet before using herbal treatments if your pet is on the following medications:

  • Steroids
  • Aspirin
  • Antibiotics
  • Cardiac drugs
  • Hormones (e.g. thyroxine)
  • Diuretics (e.g. Furosemide, Diazide)
  • Diabetic/hypoglycemic drugs (e.g. Insulin)
  • Central Nervous System drugs (e.g. phenobarbital)
  • Anti-inflammatories (e.g. Rimadyl)
  • Chemotherapy agents

References
J.A. Duke, The Green Pharmacy Herbal Handbook: Your Comprehensive Reference to the Best Herbs for Healing (Rodale Books, 2000).
C. Schwartz, Four Paws Five Directions: A Guide to Chinese Medicine for Cats and Dogs (Celestial Arts Publishing, 1996).
M.L. Wulff-Tilford and G.L. Tilford, Herbs for Pets (Bowtie Press, 1999).