By Richard Harkness
Enquirer contributor

Question: Can the herbal antidepressant St. John's wort cause the birth control pill to fail, as I've heard?

Answer: Case reports do suggest that St. John's wort could lead to unwanted pregnancies in women using oral contraceptives.

Certain liver enzymes break down the estrogen component of the pill so it can be normally removed from the body. St. John's wort is known to coax these enzymes to work faster. This causes estrogen to be removed from the body at a faster rate, thus lowering the amount of working estrogen in the blood. The effect might be like taking a weakened pill. Breakthrough bleeding could be a sign of possible contraceptive failure.

Oral contraceptives (OCs) can potentially interact with numerous other dietary supplements:

Folate: OCs can interfere with the body's absorption of folate (folic acid), though this may not cause a deficiency unless you have an increased need for this B vitamin due to repeated pregnancies, iron deficiency, malnutrition, blood loss or anticonvulsant use. Generally, however, it's probably a good idea to get extra folate by taking a general multivitamin supplement.

Vitamin B-12: OCs may lower B-12 levels, but the body seems to be able to keep the amount of B-12 at normal levels anyway. A multivitamin supplement provides B-12 if you want extra insurance.

Vitamin B-6: OCs have been reported to deplete the body of B-6, but recent studies have not found a problem. Most diets provide an adequate amount of B-6, and you can also get it in multivitamins.

Vitamin B-2: OCs may deplete vitamin B-2 to some degree, but this is unlikely to produce a deficiency under ordinary circumstances. A multivitamin supplement can provide extra insurance.

Vitamin C: OCs may depress your blood levels of vitamin C, so taking a supplement is a good idea.

Magnesium: OCs or estrogen replacement therapy may decrease your magnesium levels, especially if you don't get enough magnesium to begin with. Although a general multivitamin-mineral supplement may provide only 25 percent of the recommended daily intake of magnesium, it's not difficult to get adequate amounts from the diet.

Zinc: Oral contraceptives may reduce blood zinc levels. You will typically get 15 mg of zinc in a general multivitamin-mineral supplement.

Copper: Oral contraceptives are known to increase copper levels in the body, and there's some evidence that the latest type of oral contraceptive products may do this more so than earlier versions, apparently due to the newer progestins (progesteronelike hormones) used in them. Epidemiologic evidence suggests that high blood levels of copper may increase cardiovascular risk, so physicians may wish to keep this in mind for their patients taking OCs.

Androstenedione: This supplement might increase estrogen-related side effects. Women taking estrogen should probably avoid it.

Licorice: Licorice intake may worsen fluid retention experienced by some women taking oral contraceptives and may increase the likelihood of high blood pressure.

E-mail rharkn@aol.com.