Johns Hopkins reviews six popular herbal supplements – ginkgo, garlic, St. John’s wort, and others -- that may cause adverse interactions with prescription medication.
Many herbal dietary supplements are considered safe when used as directed, with no serious side effects reported -- yet. But problems with herbal products have been identified. It’s important to tell your doctor what supplements you use, to avoid interactions with any prescription drugs you may need to take.
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Herbal supplements contain biologically active compounds that should not be considered safe just because they are sold over the counter or come from "natural” sources such as plants. When trying a new herbal supplement, ask your doctor or pharmacist whether there are known safety issues associated with the herbal supplement, especially interactions with other medications.
A fundamental problem in assessing either the efficacy or the side effects of herbal products is the lack of strict manufacturing quality standards, allowing substantial variability of products between different manufacturers and even between different batches of one product from the same manufacturer. As a consequence, firm conclusions on these compounds are difficult to reach.
Be especially cautious before going in for surgery. Some herbal remedies appear to increase the risk of bleeding. Others may interfere with drugs commonly used before, during, and after surgery, including anesthetics. It is probably most reasonable to stop taking any dietary supplements at least a week before surgery, to give them time to “wash out” of your system.
Here are some of the more popular herbal remedies thought to interact with certain prescription drugs.
Herbal Supplement 1 – Ginkgo
Ginkgo inhibits the action of platelets in the blood, thus interfering with blood coagulation. Don’t use ginkgo if you are taking the blood thinner warfarin (Coumadin) or antiplatelet drugs such as clopidogrel (Plavix). Ginkgo may lower blood sugar, so don’t use it if you are already taking drugs for diabetes.
Herbal Supplement 2 – Garlic
Chemical compounds in garlic may inhibit blood clotting. Don’t use garlic supplements if you are already taking anticoagulants or antiplatelet drugs. Garlic can also interfere with the action of the antiviral drug saquinavir (Invirase), which is used to treat HIV infection.
Herbal Supplement 3 -- Licorice Root
Taking large amounts of licorice may cause high blood pressure and retention of water and salt. It can also deplete potassium in the body, leading to abnormal heart rhythms or symptoms of weakness or fatigue. Licorice would have the tendency to counteract the effect of some diuretics (water pills), drugs that are commonly prescribed for heart disease and high blood pressure.
Herbal Supplement 4 -- Kava
Kava appears to be toxic to the liver, so it is advisable to avoid kava altogether.
Herbal Supplement 5 -- Asian Ginseng
Asian ginseng may lower your blood sugar. Don’t use it if you are already taking diabetes drugs to lower your blood sugar. Asian ginseng may also inhibit blood clotting. Don’t use ginseng if you are already taking anticoagulants or antiplatelet drugs.
Herbal Supplement 6 -- St. John’s Wort
The problem of St. John’s wort interfering with the metabolism of many drugs is probably the best defined of all herbal interactions with other drugs. St. John's wort can interact with a variety of prescription drugs, either increasing or decreasing their effect. These drugs include the antiviral drug Invirase, the anti-rejection drug cyclosporine, the cardiac drug digoxin, the blood thinner Coumadin, antidepressants, and some cancer medications.
