Be Cautious When Taking St. John’s Wort With Other Drugs

Q: Can St. John’s wort cause the birth control pill to fail, as I’ve heard?

A: St. John’s wort, an over-the-counter herbal supplement, can be effective for milder forms of depression. Case reports do suggest that St. John’s wort could lead to unwanted pregnancies in women using oral contraceptives.

Certain enzymes break down the hormones present in oral contraceptives for elimination by the body. St. John’s wort coaxes these enzymes to work harder. This causes the hormones to be removed from the body a faster rate, thus lowering the amount of working hormones in the blood. The effect might be like taking a weakened pill. Breakthrough bleeding could be a sign of diminished pill effect and possible contraceptive failure.

Women who combine St. John’s wort with a hormonal contraceptive might wish to use an additional form of birth control.

While we’re on the subject, St. John’s wort also interacts with a number of other drugs in a similar way. Among these are the heart drug digoxin (e.g., Lanoxin) and the blood thinner warfarin (e.g., Coumadin). Blood levels of these medications must be kept within a narrow range. Slightly low levels may not work, and slightly high levels may be toxic.

 In this case, the St. John’s wort interaction is a two-edged sword with one edge hidden. Here’s what can happen: Suppose you’ve been stabilized on warfarin at a certain dose, and you start taking St. John’s wort. St. John’s wort pushes down blood levels of warfarin so that it no longer thins the blood properly. Your physician increases the dose of warfarin to regain its effect. If you then stop taking St. John’s wort, the hidden edge reveals itself.

Because St. John’s wort has been holding down warfarin levels, stopping it is like releasing the brakes, allowing drug levels to surge. The result could be excessive bleeding with possible hemorrhage.

This is a blinking caution light reminding us that “natural” (in this case, St. John’s wort) does not automatically equate with safe. Active ingredients, whether natural or Synthetic, have important effects on the body. That’s what makes them work.

Some other drugs and supplements that can interact with St. John’s wort:

Alprazolam (Xanax); Antidepressants, including amitriptyline (Elavil); nortriptyline (Pamelor, Aventyl), imipramine (Tofranil), paroxetine (Paxil), sertraline (Zoloft), fluoxetine (Prozac); fluvoxamine (Luvox); nefazodone (Serzone); Antifungals (ketoconazole, itraconazole); Anti-HIV drugs, including protease inhibitors such as amprenavir, indinavir, nelfinavir, saquinavir; NNRTIs such as nevirapine (Viramune), delavirdine (Rescriptor), efavirenz (Sustiva); Anti-migraine drugs such as sumatriptan (Imitrex); Barbiturates; Calcium blockers (diltiazem, verapamil); Clopidogrel (Plavix); Cyclosporine (Neoral, Sandimmune); Dextromethorphan (e.g., Robitussin DM); Meperidine (Demerol); Phenytoin (Dilantin); Statin drugs, including simvastatin (Zocor); atorvastatin (Lipitor); lovastatin (Mevacor); Stomach acid blockers, including cimetidine (Tagamet); ranitidine (Zantac); Tacrolimus (Prograf, Protopic); Theophylline; Tramadol (Ultram); Tryptophan; SAMe. For others, say your pharmacist or physician.

As a precaution, you should get medical advice before combining St. John’s wort with prescription or OTC products.

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(Richard Harkness is a consultant pharmacist, natural medicines specialist, and author of eight published books. Write him at 1224 King Henry Drive, Ocean Springs, MS 39564; or rharkn@aol.com. Selected questions will be used in the column.)

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