White Willow Bark

By Rania Gollakner, BS, DVM, MPH

What is white willow bark?

White willow bark is a supplement made from the bark of the white willow tree (Salix alba). The active ingredient in white willow bark is salicin, which is similar to the active ingredient in aspirin. Therefore, it is most often used to treat pain and inflammation associated with arthritis and to treat fever.

It has also been used to prevent blood clots associated with heart disease, although its effectiveness is in question for this purpose. It is used in both dogs and cats.

"It is most often used to treat pain and inflammation
associated with arthritis and to treat fever."

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

How effective is white willow bark?

Few studies in animals have been performed, but there is anecdotal evidence and limited studies in humans that show willow bark may work to treat pain, inflammation, and fever by interfering with inflammatory pathways. In humans, studies are mixed, although most show that it is effective when compared to placebo for back pain and arthritis. Evidence is lacking regarding its effectiveness as a blood thinner.

How is white willow bark given?

White willow bark is given by mouth in the form of capsules, liquid, or powder. Give with food, as dosing on an empty stomach may cause stomach upset. Measure liquid forms carefully, especially in cats.

What if I miss giving my pet the supplement?

Give the missed dose as soon as you remember, and then wait the recommended amount of time between doses. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Studies in animals are limited for this supplement and therefore information regarding side effects is also limited. Based on aspirin, side effects may include upset stomach such as vomiting and loss of appetite, and skin reactions such as rash, itching, or redness. There is some evidence that white willow bark may have fewer side effects when compared to aspirin, but more studies are needed to validate this claim.

Are there any risk factors for this supplement?

Studies in animals are limited for this supplement and therefore information regarding risk factors is also limited. Do not use this supplement in pets that are allergic to it or aspirin. Do not use white willow bark in pregnant or nursing pets, as safety has not been established. Use with caution (if at all) in pets that have asthma, breathing problems, gastrointestinal problems, stomach or intestinal ulcers, bleeding disorders, diabetes, kidney or liver disease, or skin rashes. Use this supplement with extreme caution in younger pets, as use of aspirin in human children is contraindicated. Measure doses carefully in cats, as they are more susceptible to toxicity at higher doses.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with white willow bark: blood thinners such as warfarin, non-steroidal anti-inflammatory drugs (NSAIDs), beta blockers, diuretics, methotrexate, and phenytoin.

Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this supplement?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor for adverse side effects.

How do I store white willow bark?

In general, store this supplement in a cool place, protected from light and moisture. There are many different manufacturers and formulations of this supplement, so always follow the storage instructions on the label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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