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St. John’s Wort

By

Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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Topic Resources

The reddish substance in the plant’s flowers contains numerous biologically active compounds, including hypericin and hyperforin. (See also Overview of Dietary Supplements.)

Medicinal claims

People take St. John’s wort mostly to relieve symptoms of depression. Study results vary, but there may be a benefit in treating mild to moderate short-term depression. Overall, some studies show St. John’s wort may benefit people with mild to moderate depression and may be as effective as some traditional antidepressants. However, St. John's wort is not effective for major depression.

St. John’s wort has been used in the treatment of skin disorders, including psoriasis, and attention-deficit/hyperactivity disorder (ADHD) in children, but its effectiveness in treating these disorders is unproved.

Possible side effects

St. John’s wort may cause increased sensitivity to sunlight. Other side effects include dry mouth, digestive tract symptoms, fatigue, confusion, and mania (in people with bipolar disorder).

Pregnant women should not take this supplement because it increases muscle tone in the uterus and thus may increase the risk of a miscarriage.

Possible drug interactions

One of the larger problems with St. John’s wort is that it may interact negatively with a number of drugs people take (see table Drug Interactions With St. John's Wort). These interactions may lead to toxic reactions or ineffectiveness of the drug.

Table
icon

Drug Interactions With St. John's Wort

Affected Drugs

Interaction

Benzodiazepines

St. John’s wort may reduce the effectiveness of these drugs in reducing anxiety and may increase the risk of side effects such as drowsiness.

Cyclosporine

St. John’s wort may reduce blood levels of cyclosporine, making it less effective, with potentially dangerous results (such as rejection of an organ transplant).

Digoxin

St. John’s wort may reduce blood levels of digoxin, making it less effective, with potentially dangerous results.

Iron

St. John’s wort may reduce iron absorption.

Monoamine oxidase inhibitors (MAOIs)

St. John’s wort may intensify the effects of MAOIs, possibly causing very high blood pressure that requires emergency treatment.

Nonnucleoside reverse transcriptase inhibitors

St. John’s wort increases the metabolism of these drugs, reducing their effectiveness.

Oral contraceptives

St. John’s wort increases the metabolism of these drugs, reducing their effectiveness.

Omeprazole

St. John’s wort decreases serum concentrations of omeprazole, reducing its effectiveness.

Photosensitizing drugs (such as  amiodarone, naproxen, sulfonylureas [such as glipizide], and sulfonamide antibiotics)

When taken with these drugs, St. John’s wort may increase the risk of sun sensitivity.

Protease inhibitors (such as indinavir or saquinavir), which are used to treat human immunodeficiency virus [HIV] infection

St. John’s wort may reduce blood levels of protease inhibitors, making them less effective.

Selective serotonin reuptake inhibitors (SSRIs, such as fluoxetine, paroxetine, and sertraline)

St. John’s wort may intensify the effects of these drugs.

Tricyclic antidepressants

St. John’s wort may decrease the effects of these drugs.

Warfarin

St. John’s wort may reduce blood levels of warfarin, making it less effective and clot formation more likely.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

Generic Name Select Brand Names
NEORAL, SANDIMMUNE
ZOLOFT
INVIRASE
CORDARONE
PRILOSEC
PAXIL
PROZAC, SARAFEM
GLUCOTROL
CRIXIVAN
ALEVE, NAPROSYN
COUMADIN
LANOXIN
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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