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Chapter: Modern Pharmacology with Clinical Applications: Herbal Medicine

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Herbal Preparations: St. John’s Wort

St. John’s wort (Hypericum perforatum) is a yellow-flowered perennial European herb that has become widely naturalized in the United States.

St. John’s Wort

 

St. John’s wort (Hypericum perforatum) is a yellow-flowered perennial European herb that has become widely naturalized in the United States. Its name is derived from the Old English word for plant, wort, and from the fact that it often starts blooming around June 24, St. John’s day. Although St. John’s wort has tradi-tionally been used for wound healing, insomnia, rheumatism, and depression, it is most popular today for the treatment of mild to moderate depression.

 

The leafy parts of the herb contain naphthodi-anthrones (e.g., hypericin), flavonoids (e.g., quercetin), and phloroglucinols (e.g., hypaphorine). Although this herb is now commonly standardized for its hypericin content, it appears that its other constituents may also be just as pharmacologically active.

 

Mechanism of Action

 

Just how St. John’s wort treats depression is not clearly understood. It is possible that this herb’s various com-ponents may work synergistically rather than through a single active substance, mimicking the action of tradi-tional antidepressants. High concentrations can affect in vitro serotonin reuptake, but it is unclear whether this would occur in a patient taking standard oral doses. The hypaphorine constituent may possess serotonin reup-take inhibitor activity, and it also inhibits synaptic up-take of amino butyric acid (GABA) and L-glutamate. Earlier studies demonstrated some monoamine oxidase inhibition, but this action now seems unlikely to be clin-ically relevant. Flavonoid components and hypericin also may weakly inhibit catechol-O-methyl-transferase (COMT). Melatonin, surprisingly, has also been identi-fied in St. John’s wort and may play a role in its sleep-enhancing and antidepressant effects.

 

Indications

 

St. John’s wort is very popular as a physician-prescribed antidepressant in Europe and is widely used for this purpose—usually without medical guidance—in the United States. A meta-analysis of 23 studies concluded that St. John’s wort was more effective than placebo in treating mild to moderate depression and was as effec-tive as imipramine and standard antidepressants. It was also better tolerated than the antidepressants to which it was compared. A recent meta-analysis, however, failed to find St. John’s wort effective for severe depres-sion.

 

 

Adverse Reactions, Contraindications, and Interactions

 

St. John’s wort is usually well tolerated, but insomnia, dizziness, fatigue, restlessness, GI upset, constipation, dry mouth, and allergy are reported as possible side ef-fects. Hypomania has also been reported in several cases, and rarely, photosensitivity can be a problem fol-lowing high doses; hypericin seems to be the component responsible for the photosensitivity. Sun-induced neuropathy has also been described, and it is possible that hypericin may also increase the risk of cataracts with prolonged use. While a prior allergy to the herb is the main contraindication, St. John’s wort should also be avoided in pregnant and breast-feeding women (it may increase uterine tone) and in children until its safety is further established.

 

A major emerging concern in St. John’s wort use is the numerous clinically significant herb–drug interac-tions that have been reported. St. John’s wort appears to be a major inducer of the cytochrome P450 3A4 (CYP3A4) enzyme system in the liver. This first came to light following acute heart transplant rejection in a per-son taking cyclosporin and St. John’s wort. The cy-closporin levels remained subtherapeutic until St. John’s wort was discontinued. A similar phenomenon was noted with AIDS patients taking protease inhibitors and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Concomitant use of St. John’s wort reduced the effectiveness of these medicines as well. Since then, St. John’s wort has been shown to reduce plasma levels of digoxin, warfarin, theophylline, and oral contracep-tives. Breakthrough bleeding has been observed in young women taking this herb, and patients starting oral contraceptives should be counseled to use backup contraception if they take St. John’s wort or antibiotics. St. John’s wort can adversely affect many other com-mon medications, including nonsedating antihistamines, antifungals, chemotherapeutic agents, and calcium chan-nel blockers.

 

SSRIs should not be taken with St. John’s wort be-cause of the risk of the onset of a serotonin syndrome characterized by nausea, tremor, and weakness. Alcohol also should be avoided. St. John’s wort can increase opioid-induced sleep.

 

Dose

 

St. John’s wort is commonly used at 300 mg of extract (standardized to 0.3% hypericin) three times daily for 6 weeks or longer. Short-term treatment is usually inef-fective.

 

Conclusion

 

St. John’s wort is probably effective for mild to moder-ate but not severe depression. Although well tolerated in most patients, a major concern is its numerous herb–drug interactions mediated by its induction of the cytochrome P450 enzyme system.

 

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