Recent news reports revealed that St. John's Wort, a popular herbal mood elevator, may interact with a number of prescription drugs. While presented as a bolt out of the blue, the fact is that some popular supplements and common foods can influence the uptake and metabolism of prescription drugs. For instance, a compound found in grapefruit influences a liver enzyme (cytochrome P450), which regulates how fast the body eliminates a host of compounds, including many prescription drugs. Black pepper can have a similar effect. Therefore, it is hardly surprising that anti-oxidants similarly can influence how the body responds to prescription drugs -- and vice versa.

Anyone who is taking prescription medications should make certain that the dispensing physician has given a green light to the addition of herbs and other supplements to their diet. Pharmacists have special manuals, which include the latest information on prescription drug interactions and contraindications. As in the case of grapefruit, otherwise entirely safe items can have unwanted effects if taken in conjunction with the wrong medications.

As a general rule, any supplements taken during pregnancy and lactation should be discussed with a health care professional. Anti-oxidant vitamins and herbs typically are remarkably safe, but even these should be discussed with a knowledgeable physician.

Alpha-lipoic Acid
The powerful anti-oxidant may strongly intensify the action of insulin. Those taking diabetic medications should exercise caution. Those who are deficient in vitamin B-1 should not take it.

Beta-carotene and Other Carotenoids
Beta-carotene is the only one of the commonly supplemented carotenoids that has any significant unwanted interactions. Chronic high levels of supplementation may reduce the amount of vitamin E in the system. Beta-carotene also has a negative interaction with alcohol. The other carotenoids, including lutein, lycopene and zeaxanthine, appear to be safe and without drug interactions.

The Coenzyme Q10
Other than its speculated interaction with anticoagulants (see below), coenzyme Q10 is not known to interfere with any drug. However, many drugs substantially reduce the body's own stores of coenzyme Q10. Sulfonylureas (a class of diabetic drugs), statin drugs (to lower cholesterol) and beta-blockers (to lower blood pressure) all may deplete coenzyme Q10 or interfere with coenzyme Q10-dependent enzyme systems. Those who suffer from disturbed sleep should exercise caution when supplementing with larger doses.

Cysteine
May alter the metabolism of insulin. Diabetics on insulin or medications may find that supplementing with this compound can change the required dosage.

Vitamin C
Vitamin C is considered to be very safe. The just released guidelines of the Institute of Medicine of the National Academy of Sciences presents two grams per day to be an upper limit of intake beyond which individuals may begin to experience an increased laxative effect because of the acidity of the vitamin. Drug interactions are rare. Individuals taking medications for glucose-6-phosphate dehydrogenase deficiency, or who suffer from a history of kidney stones or kidney failure, including those taking medications for these conditions, should consult a health care professional if taking more than approximately 250 mg per day. Vitamin C may enhance the absorption of aluminum, and therefore should not be ingested together with aluminum-containing preparations, such as many products taken for heartburn. Two other conditions sometimes mentioned in connection with vitamin C both involve the mineral iron. Iron overload (hemosiderosis or hemochromatosis) is a condition in which additional vitamin C normally must be avoided. Also, some antibiotics work by binding iron to inhibit bacterial growth. An elevated intake of vitamin C may reduce the effectiveness of such antibiotics. Vitamin C increases the absorption of iron, decreases the absorption of copper, and may interfere with a blood test for levels of vitamin B-12.

Vitamin E
As is true of vitamin C, vitamin E is considered to be very safe. The just released guidelines of the Institute of Medicine of the National Academy of Sciences present 1,500 IU per day to be a safe upper limit of intake. Beyond this level, vitamin E's anticoagulant properties become significant with effects difficult to predict. (See below regarding warfarin, aspirin and anticoagulants.) Vitamin E appears to improve cardiac tone/stroke volume. Individuals with high blood pressure should only slowly increase their intake of vitamin E under the guidance of their physician to allow adjustment by the body. Inasmuch as vitamin E reduces insulin requirements, diabetics should supplement with caution and begin with 100 IU or less per day. Some reports indicate that supplementation at 800 IU per day can cause muscle weakness in some small number of individuals. Similarly, there are reports of doses of 600 IU or more per day causing a decrease in thyroid hormone release in some subjects. These last two types of reports are extremely rare, but those with problems involving creatine kinase or below par thyroid function should keep them in mind.

Hawthorn
Although this herb by itself is quite safe and an excellent source of anti-oxidant factors, it possesses some cardiotonic properties and is ill advised for use in conjunction with cardiac drugs, such as digoxin.

Melatonin
Should not be used by those who are taking medications, such as prednisone, which are intended to control autoimmune responses. Similarly, melatonin may interact with medications used to alter mood, both depression and mania. Melatonin may intensify the effects of drugs that influence brain serotonin levels.

Warfarin (Coumadin®), Aspirin, and Other Anticoagulants
Anticoagulants are given to reduce platelet "stickiness" to prevent damage to artery walls and to prevent the formation of clots in the circulatory system, which might come to block blood flow. Many anti-oxidants and anti-oxidant sources also reduce platelet aggregation and thus may have an additive effect if taken with warfarin, aspirin or other "blood thinners." These include vitamin E, garlic, ginger and ginkgo biloba and possibly vitamin C. Some herbs contain compounds that are similar in structure to warfarin and may augment its effects. The more common of these are dong quai, fenugreek, horse chestnut, red clover and sweet clover. Conversely, sources of vitamin K can inhibit the actions of warfarin. Some prized anti-oxidant vegetables (broccoli, Brussels sprouts, kale, parsley, spinach, and others) are high in vitamin K. Coenzyme Q10 also may interfere with the actions of warfarin. The minerals iron, magnesium and zinc may bind to warfarin and prevent its absorption.

The foregoing list is hardly exhaustive. However, it does give a sense that one can take too much of even a "safe" supplement. Moreover, it is always necessary to proceed with caution if planning to supplement with vitamins and/or herbs when taking prescription medications.

Dallas Clouatre, PhD, is a contributing expert to anti-oxidant.com and the author of several books on nutritional supplements.

Selected References

Garrison, Robert Jr., and Elizabeth Somer. The Nutrition Desk Reference. (1995)
Hausman, Patricia. The Right Dose: How to Take Vitamins & Minerals Safely. (1987)
Marshall, Charles W. Vitamins and Minerals: Help or Harm? (1985)
Miller, Lucinda G. and Wallace J. Murray, editors. Herbal Medicinals: A Clinician's Guide. (1998)

Pages: 12Continue Reading