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y Ernest B. Hawkins, R.Ph.　　

Gentle, natural herbs have gained a reputation as being able to do no wrong. Most people consider them safe healing agents without the side effects of prescription drugs. And overall, herbs generally are safe when used appropriately in recommended doses. But, as with any medicine, there are points to keep in mind when taking them therapeutically.

For all their good, some commercially available herbs have potentially problematic constituents. For example, comfrey (Symphytum officinale) and coltsfoot (Tussilago farfara) contain alkaloids that, when taken in high doses, can be toxic to the liver.1 Commonly used herbs such as ginkgo (Ginkgo biloba) and horse chestnut (Aesculus hippocastanum) may increase chances of bleeding, especially if taken with anticoagulant medications.2,3 Sedative herbs such as valerian (Valeriana officinalis) and kava (Piper methysticum) can interact with sedative prescription drugs by increasing their effects.4,5 Taking these and other herbs that have potential interactions with drugs can cause unwanted side effects and may necessitate medical treatment.

Certain herbs such as black cohosh (Cimicifuga racemosa) and St. John's wort (Hypericum perforatum) may be harmful during pregnancy and lactation because of their potential to stimulate the uterus and cause a miscarriage.6,7 Likewise, diabetics on insulin should use caution when taking bitter melon (Momordica charantia) because it has the potential to lower blood sugar levels.8 Licorice (Glycyrrhiza glabra) should be avoided by those with high blood pressure because the herb can antagonize and lead to hypertension.9

Beyond potential effects like these, some herbs may deplete the body of important vitamins and minerals.

A pharmacist or health care professional can determine the appropriate use of herbs for people taking prescription medications or for those with pre-existing conditions. But as a savvy consumer, you should educate yourself about potential depletions or interactions. Most herb/nutrient depletion information is based on research, medical observation and theoretical interactions deduced from pharmacological properties of herbs. Following are some possible depletions.

Herbs That Take Away
Black cohosh, grape seed (Vitis vinifera), green and black teas (Camellia sinensis), hawthorn (Crataegus spp.), horse chestnut, saw palmetto (Serenoa repens), St. John's wort and valerian contain an acid called tannin. Tannins can theoretically alter the absorption of calcium, copper, iron, magnesium and zinc. More research is needed to determine if this is a significant problem.

If you regularly take tannic herbs, do so either one hour before or two hours after taking vitamin and mineral supplements that include calcium, copper, iron, magnesium or zinc.

Horsetail (Equisetum arvense), celery seed (Apium graveolens), dandelion leaf (Taraxacum officinale) and elder flower (Sambucus nigra, S. canadensis) are generally used as diuretics to rid the body of excess fluid. Diuretic herbs are commonly used during detoxification and for conditions such as high blood pressure, kidney infections, obesity and swelling associated with premenstrual syndrome.10

Diuretic supplements may cause fluid electrolyte imbalances due to the loss of water, sodium and chloride, especially if used for longer than two weeks. The danger is heightened when diuretics are used chronically in amounts that exceed the recommended dosages. Only doctors should recommend diuretic herbs to individuals with pre-existing medical conditions, especially those already on diuretics. People taking diuretics should replace fluid and electrolytes with liquids that have a low sugar content.

Horsetail is used to treat bone fractures, connective tissue damage, osteoporosis and tooth and nail injuries because it contains silicic acid, a constituent that provides elemental silicon.11 Reports suggest horsetail supplements deplete the body of thiamine (vitamin B1) because they contain an enzyme that may destroy thiamine.12 This B vitamin helps the body produce energy and nourishes the nervous system.13 Thiamine deficiency symptoms include appetite loss, fatigue, nausea, and mental disturbances such as depression and memory loss.

Take a multivitamin containing 10-50 mg of thiamine either one hour before or two hours after taking horsetail. Brown rice, navy beans, salmon, soybeans and whole grains are also sources of thiamine.

Kava is a popular dietary supplement traditionally used to manage anxiety and restlessness and to relax skeletal muscles. It also may be useful for treating epilepsy.14 Chronic and heavy use of kava has occasionally been reported to cause a scaly, yellow skin rash that disappears after discontinuation of the herb.15 The rash resembles one brought on by a niacin deficiency; however, a double-blind, placebo-controlled study showed no change in the rash after niacin supplementation.16 Until more is known, however, people taking kava regularly may also wish to take a multivitamin with at least 50-100 mg of niacin daily.

Licorice root is commonly used as an adrenal tonic, expectorant and demulcent because of its mucous membrane-soothing action.17 Glycyrrhizin, the active component in licorice, can cause sodium retention as well as hypertension and other cardiac problems.18 When glycyrrhizin is removed, the result is called deglycyrrhizinated (DGL) licorice, which is used to treat peptic ulcers.17

If you take heart medications or have pre-existing medical conditions such as heart, kidney or liver disease, take licorice products only under a doctor's supervision. Those taking licorice supplements may benefit from a multivitamin with adequate potassium. Dietary sources of potassium include avocados, bananas, lentils and spinach.

Senna (Cassia senna) and other laxative herbs including aloe (Aloe spp.), cascara sagrado bark (Rhamnus purshianus) and yellowdock root (Rumex crispus) can negatively affect the absorption, metabolism and excretion of nutrients, drugs and other dietary supplements.19

When taking laxatives, use them for no more than 48 hours. If constipation is not alleviated within that time, consult your doctor. Long-term laxative use can cause electrolyte imbalances as a result of lost water, sodium, potassium and other minerals.

Also, don't use laxatives when abdominal pain is present, especially if it has any of the following characteristics: localizes to a specific area of the abdomen or radiates from a particular part of the abdomen; is accompanied by sudden onset of nausea/vomiting, constipation, fever, appetite loss, or bloating; is unlike previously experienced abdominal pain; or is painful with movement. These types of pain should be addressed by a physician.

Education is Key
For reasons that range from an increased sense of personal responsibility to exorbitant health care costs, people are taking a more active role in their health and the health of their loved ones. But when you turn to supplements, make sure you know what it is you are taking, how it works, and if it's okay to take with other medications. Your pharmacist or health care provider should be an excellent source of education. Always ask them for more information.