St. John's wort has been used for centuries to treat mental disorders and nerve pain.

In ancient times, herbalists wrote about its use as a sedative and a treatment for malaria, as well as a balm for wounds, burns, and insect bites.

Today, St. John's wort is used by some for depression, anxiety, and/or sleep disorders.

The flowering tops of St. John's wort are used to prepare teas and tablets containing concentrated extracts.

There is some scientific evidence that St. John's wort is useful for treating mild to moderate depression. However, two large studies, one sponsored by NCCAM, showed that the herb was no more effective than placebo in treating major depression of moderate severity.

NCCAM is studying the use of St. John's wort in a wider spectrum of mood disorders, including minor depression.

St. John's wort may cause increased sensitivity to sunlight. Other side effects can include anxiety, dry mouth, dizziness, gastrointestinal symptoms, fatigue, headache, or sexual dysfunction.

Research shows that St. John's wort interacts with some drugs. The herb affects the way the body processes or breaks down many drugs; in some cases, it may speed or slow a drug's breakdown. Drugs that can be affected include:

Indinavir and possibly other drugs used to control HIV infection

Irinotecan and possibly other drugs used to treat cancer

Cyclosporine, which prevents the body from rejecting transplanted organs

Digoxin, which strengthens heart muscle contractions

Warfarin and related anticoagulants

Birth control pills

Antidepressants

When combined with certain antidepressants, St. John's wort may increase side effects such as nausea, anxiety, headache, and confusion.

St. John's wort is not a proven therapy for depression. If depression is not adequately treated, it can become severe. Anyone who may have depression should see a health care provider. There are effective proven therapies available.

It is important to inform your health care providers about any herb or dietary supplement you are using, including St. John's wort. This helps to ensure safe and coordinated care.