Combining dietary supplements and medications can have dangerous and even fatal effects. Many people take both dietary supplements and prescription or over-the-counter medications, but few are unaware of the potential interactions between them. Some supplements can decrease the effects of medications, while others can increase the effects, including unwanted side effects, of medications. Unfortunately, in the case of many drugs and supplements, there is currently little information on potential interactions and more research is needed.
This article will discuss 6 things to know about herbs that have a high risk of possible interactions with certain medications. Nearly 25% of adults in the United States report taking a prescription medication with a dietary supplement. St. John's Wort and golden seal are known to cause clinically important drug interactions and should be avoided by most patients receiving any drug treatment.
However, many other supplements are expected to cause interactions based solely on in vitro studies that have not been confirmed or refuted in human clinical trials. Some supplements may cause interactions with some medications, but are likely to be safe with other medications (e.g., ginkgo biloba). Some supplements have a low chance of drug interactions and, with certain caveats, can be safely taken with most medications (e.g., garlic). Physicians should consult reliable resources on dietary supplements, or from clinical or pharmaceutical pharmacists, to help evaluate the safety of specific combinations of herbal supplements and drugs. Since most patients do not disclose the use of supplements to doctors, the most important strategy for detecting herbal and drug interactions is to develop a relationship of trust that encourages patients to discuss the use of dietary supplements. Estimates show that between 40 and 60% of adults in the United States with chronic diseases consume dietary supplements and, among patients taking prescription medications, it is estimated that between 20 and 25% use a dietary supplement concurrently. The National Center for Complementary and Integrative Health defines dietary supplements as a variety of products, including herbs, vitamins and minerals, and probiotics.
This review focuses on drug interactions with herbal dietary supplements, which are defined as supplements that contain whole plant extracts or that are consumed in the form of powder, capsules, tablets, or liquid formulations. Clinically important interactions between an herbal supplement and a drug usually manifest as pharmacokinetic interactions, affecting the concentration of a drug in the blood and the pharmacological action. In many cases, pharmacokinetic interactions can be safely counteracted by adjusting the dose of the drug. The risk of pharmacokinetic interaction occurs when an herbal supplement shares the same absorption, distribution, metabolism, or excretion mechanism (ADME) as a concomitantly administered drug. Less commonly, herbal and drug interactions can manifest as pharmacodynamic interactions, which involve direct pharmacological actions of an herbal supplement that are not related to changes in blood concentrations. The risk of pharmacodynamic interaction occurs when an herbal supplement has a direct effect on the mechanism of action of a co-administered drug.
The direct pharmacological effects of an herbal supplement can antagonize or exacerbate the clinical effects of the drug without changing the concentration of the drug. In most cases, a change in the dosage of the drug will not counteract the pharmacodynamic interaction between herbs and drugs. Drug interactions are initially evaluated by in vitro systems. Although in vitro evaluations are highly sensitive and can be used to rule out possible interactions between herbs and drugs, it is important to follow up positive results in vitro with a human clinical trial to estimate the possible impact of an interaction on clinical outcomes. Many positive in vitro interactions have not been confirmed in human trials, which highlights the importance of confirming potential interactions. In several clinical trials in humans, it has been demonstrated that black cohosh (Actaea racemosa) has no clinically significant effects on multiple CYP and P-GP enzymes.
However, there is potential concern about interactions with OATP2B1 which could reduce the effectiveness of drugs such as amiodarone, fexofenadine (Allegra), glyburide and many statin drugs. Echinacea (Echinacea purpurea) has shown no inhibitory or inductive effects on CYP2D6, CYP2C9 or P-gP in human studies. However, there are conflicting results on CYP1A2 and CYP3A4 even with potentially use with use in the short term. For this reason care must be taken when combining echinacea with medications that are metabolized by any of these CYP enzymes including antipsychotic and antidepressant medications. Goldenseal (Hydrastis canadensis) has been shown to inhibit two major metabolic enzymes CYP2D6 and CYP3A4 which are responsible for the metabolism of more than half of the pharmaceutical agents currently in use.
Although some goldenseal drug combinations may be safe until data from other human clinical trials are available doctors should recommend not using goldenseal in combination with most other medications. Several human studies have demonstrated that kava kava (Piper methysticum) has no effect on CYP1A2 CYP2D6 CYP3A4 or P-gp. In a study with human volunteers kava inhibited CYP2E1 which participates in the metabolism of several anesthetic agents as well as on acetaminophen. In addition two in vitro studies suggest potential inhibition of CYP2C9 and CYP2C19 metabolism which are involved in the metabolism of several anaesthetic agents many non-steroidal anti-inflammatory drugs blockers of angiotensin glipizide (Glucotrol) glyburide and rosiglitazone (Avandia) valproic acid (Depakene) warfarin proton pump inhibitors phenytoin (Dilantin) and clopidogrel (Plavix).
Patients taking medications that are metabolized by CYP2C9 or CYP2C19 should be closely monitored for clinical adverse effects and laboratory abnormalities. Caution should be used in patients who use central nervous system depressants such as benzodiazepines or alcohol because of increased risk for somnolence and depression when combined with certain herbs like kava kava St John's Wort valerian root passionflower hops chamomile lavender skullcap catnip lemon balm magnolia bark California poppy yerba mansa Jamaican dogwood wild lettuce lobelia blue cohosh guarana yohimbe ephedra ma huang bitter orange extract caffeine guarana yerba mate cola nut kola nut guarana extract green tea extract black tea extract mate tea extract oolong tea extract white tea extract coffee bean extract cocoa bean extract cocoa extract chocolate extract cocoa powder chocolate powder caffeine powder guarana powder...
