St. John's Wort

By Rania Gollakner, BS, DVM, MPH

What is St. John’s wort?

St. John’s wort is an herbal supplement made from the Hypericum perforatum plant. It has been traditionally used for pain, but now is also used for depression and anxiety disorders. Other possible uses for this supplement include anti-inflammatory, antimicrobial, and wound healing effects. In addition to humans, it is most commonly used in dogs and cats.

"It has been traditionally used for pain, but now is also used for depression and anxiety disorders."

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 St. John’s wort?

Limited studies in companion animals have been performed, but there is anecdotal evidence that St. John’s wort works to treat depression, anxiety, inflammation, and pain by modulating brain chemicals and other mechanisms. In humans, scientific studies are mixed, with many showing positive results in treating depression and other conditions, but with others showing no difference when compared to a placebo.

How is St. John’s wort given?

St. John’s wort is given by mouth in the form of a capsule, tablet, liquid extract, or powder. Give this supplement with food. Measure liquid forms carefully. Do not give more than prescribed by your veterinarian.

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 are limited in companion animals for this supplement and therefore information regarding side effects is also limited. Side effects may include vomiting, diarrhea, dry mouth, skin reactions (redness, itchiness, and sun sensitivity, especially in animals with white skin), allergic reactions (facial swelling or hives), restlessness, or sleepiness. Side effects are more likely to occur with higher doses.

Are there any risk factors for this supplement?

Studies are limited in companion animals for this supplement and therefore information regarding risk factors is also limited. Do not use St. John’s wort in pets that are allergic to it, very old or young pets, or pets that are pregnant or nursing. It should be used cautiously in pets with liver, kidney, or heart disease.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with St. John’s Wort: amitriptyline, antifungals, antihypertensives (high blood pressure medications), antivirals, benzodiazepines, chemotherapies, cyclosporin, digoxin, fexofenadine, imatinib mesylate, ivabradine, monoamine oxidase inhibitors (MAOIs), selective serotonin reuptake inhibitors (SSRIs), tacrolimus, tricyclic antidepressants, and warfarin.

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.

How do I store St. John’s wort?

In general, store this supplement in a cool, dry place, protected from light. There are many formulations and manufacturers of St. John’s wort, so always follow the specific storage instructions on the product 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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