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ST. JOHN’S WORT is not just for anxiety; it is effective in cancer and infections.

The active components are found in the buds, flowers, and newest leaves. Extracts are usually standardized to the substance hypericin, which has led to the widespread misconception that hypericin is the active ingredient.

However, there is no evidence hypericin is an antidepressant. Recent attention has focused on another ingredient named hyperforin as the potential active ingredient. It appears that standard St. John’s wort extract contains about one to six percent hyperforin.

We don’t really know how St. John’s wort works. Early research suggested it worked like the oldest class of antidepressants, the MAO inhibitors. However, later research discredited this idea. More recent research suggests it may raise levels of serotonin, norepinephrine, and dopamine. This probably increases neurotransmitters to maintain normal mood and emotional stability. The herb may also cause binding of GABA and act as a serotonin reuptake inhibitor. Studies have used the standardized extract containing 0.14 percent hypericin.

Evidence from animal and human studies suggest hyperforin is the ingredient that raises these neurotransmitters. However, there may be other active ingredients in St. John’s wort also at work.

Therapeutic Uses
The herb has been recommended for depression, separation anxiety, and certain forms of aggression in pets.

In people, it is one of the best-documented herbal treatments with a scientific record approaching that of many prescription drugs. It is a prescription antidepressant in Germany, covered by the national healthcare system, and is prescribed more frequently for depression than any synthetic drug.

It is also useful for its antiviral and antibacterial properties. It also has tonic effects on nerves.

Interest in St. John’s wort is ongoing regarding antiviral activity and the potential to treat diseases, including both human and feline AIDS infections. While definitive proof is lacking, it may be worthwhile to try St. John’s wort in pets with severe viral infections (distemper, feline leukemia, immunodeficiency infections).

Applied locally, this herb is useful to heal wounds.

In people, the current recommendation is 300 mg three time daily of the 0.3 percent hypericin standardized solution as treatment for depression. A few products on the market are standardized to hyperforin content (usually three to five percent) instead of hypericin. These are taken at the same dosage.

In dogs, a dose of 250 to 300 mg twice daily for large dogs has been recommended.

Scientific Evidence
In people, research suggests St. John’s wort is effective in about 55 percent of cases. As with other antidepressants, the full effect takes approximately four to six weeks to develop. Although St. John’s wort appears to be somewhat less powerful than standard antidepressants, it rarely causes side effect.

Safety Issues
Use of St. John’s wort may potentiate anesthetics and other sedatives; photosensitivity has been reported in people taking high doses. The herb should not be taken with other drugs that can inhibit MAO. In people, it is recommended to take the herb with food to decrease gastrointestinal upset. (Mild stomach discomfort, allergic reactions like a rash, lethargy, and restlessness.)

Animal studies involving very large doses for 26 weeks have not shown any serious effects.

Do not combine St. John’s wort with prescription antidepressants, especially drugs that increase serotonin levels, except on the specific advice of a veterinarian. Since some antidepressants, such as Prozac, linger in the blood for quite some time, caution is advised when switching from a drug to St. John’s wort. Since no one knows whether it is absolutely safe to combine the herb with medications, the safest approach is to stop administering similar medications and allow them to wash out of your pet’s system before starting St. John’s wort. Consult with your vet on how much time is necessary.

There has also been an informal report of St. John’s wort lowering blood levels of theophylline, an asthma medication, in people. Preliminary investigation suggests the hypericin in the herb may increase the activity of a liver enzyme called cytochrome P-450. Because this enzyme can break down drugs, St. John’s wort may cause the body to speed the breakdown of various drugs, thereby decreasing their effectiveness.

Finally, reports from the University of Colorado suggest St. John’s wort may interfere with the action of the anti-tumor drugs etoposide (VePesid), teniposide (Vumon), mitoxantrone (Novantrone), and doxorubicin (Adriamycin).

Safety in young children, pregnant or nursing women, or those with severe liver or kidney disease has not been established. Similar precautions in pets are probably also warranted.

Shawn Messonnier, DVM

As my thank you for reading my articles, enter code “drshawn” at my natural products web store,, to save 10% on all your future purchases!

Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!

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