Assessing product safety and quality
Using the available metabolic data, it is important to assess the potential for unfavorable drug interactions between the supplement and any prescription pharmaceuticals the patient may be taking. This task can be difficult because many herbals lack accurate pharmacokinetic data. However, certain assumptions can be made.Prescription drugs involving the hepatic cytochrome P-450 enzyme system, for example, should be closely analyzed since many additive chemicals in herbal preparations will lead either to potentiation or inhibition of that system. This can, in turn, result in dangerously high or low levels of the drug.
The clinician should be especially aware of an additive supplement if a patient is taking warfarin, as this drug is highly metabolized in the P-450 enzyme chain. An unscientific but seemingly reliable rule of thumb for herbals and warfarin is the “Rule of Gs”: that is, any herbal supplement beginning with the letter G is likely to interfere with warfarin metabolism. Garlic, ginger, ginkgo biloba, ginseng, and green tea are all prone to interact adversely with warfarin either by interfering with platelet aggregation or other metabolic steps in the coagulation process.6
Once drug interactions are examined, product quality must be assessed. The sources of herbal products are as varied as the label names, and quality has been shown to be widely inconsistent even when there is only one manufacturer. One study found a fourfold variation in active-ingredient content of selected goldenseal herbal preparations, with only 10 of 17 meeting proposed U.S. Pharmacopeia (USP) standards.7 A European review of echinacea products on the German market found “wide variations in levels of tested phytochemical components,” and 44% of the products on the U.S. market did not pass the criteria set by ConsumerLab for its quality review.8
A variety of factors account for such inconsistencies. For example, it is impossible to determine with any assurance where the product was grown and under what conditions. The use of fertilizers, pesticides, and herbicides is usually unknown, but these have a major impact on the safety and purity of the product. Because there are no standardizations in place for dosages, labeling recommendations are guidelines, at best. And finally, the chemical potency of any single batch of herbals may or may not be sufficient to produce a therapeutic effect or be safe.
After harvesting, the processing of the plant comes into question. Types of capsule material, cleanliness of the manufacturing area, and consistency of product all should be monitored. Although the FDA has no regulatory control over efficacy, Good Manufacturing Practices (GMPs) are the gold standard for assessing this manufacturing quality.4 GMPs address all areas of the manufacturing process. Physical-plant construction, cleanliness, maintenance, and quality checks are logged and reported. Outliers are accounted for, and persistent problem areas are identified, accompanied by action plans for resolution. While the industry is basically unregulated, any manufacturer of products for human consumption should be held to the GMP or an equivalent standard for basic safety reasons.
Before a particular source for herbals can be recommended, the manufacturer should be evaluated. Detailed information regarding quality management of the products distributed is available on the Internet. Investigate technical-education departments that answer product-related questions; evidence-based references should be cited in any responses. Finally, manufacturers should be readily forthcoming with information on the quality management of their processing and distribution facilities.
Product labeling should consist of the following9:
- Name of the supplement
- Net quantity of contents (e.g., 50 tablets)
- Disclaimer (e.g., “This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.”)
- Supplement facts panel, which includes serving size, active ingredient, and amount of active ingredient
- A complete list of additional ingredients (usually with no established recommended daily value)
- Name and address of manufacturer, packer, or distributor
- The USP Dietary Supplement Verified seal should be prominently displayed. This indicates that the supplement has met certain manufacturing standards.
Once product labeling has been examined, it is important that only single-herb supplements be recommended instead of combinations. When multiple herbs are used in a single product, determining allergies or other serious interactions becomes almost impossible. Patients with pre-existing botanical allergies should avoid all herbal products because the potential for a serious reaction exists. In addition, patients who are scheduled for any surgical procedure should discontinue herbals at least one week before because many herbs can affect coagulation times. Also, little is known about the interaction of herbs with anesthesia.
Another important factor to consider when recommending herbal products is cost. Even though these supplements are not prescription drugs, many come with fairly sizable price tags. When more than one, or as is often the case, several herbs are being used, they can become quite costly. Patients can easily find themselves spending nearly as much for herbals as they would for some prescription drugs, especially since herbals aren’t covered by insurance. Additionally, most herbal literature cautions consumers not to expect to see significant results for at least a month, sometimes longer.
Finally, some herbal supplements have failed to show any benefit sufficient to outweigh the potential for toxic side effects. These should always be discouraged and never recommended. The most common of these are10:
- Ephedra: potential for serious palpitations, tachycardia, and increased BP. Of note, in 2004, the FDA banned all U.S. sales of dietary supplements containing ephedra, also known as “ma huang.”
- Chapparal: can cause liver failure
- Comfrey: known to cause liver failure and cancer
- Lobelia: can induce respiratory failure, tachycardia, and hypertension
- Yohimbe: induces anxiety, hypertension, nausea, vomiting, and, in extreme cases, renal failure
Whether or not we like these products, clinicians must acknowledge the prevalence of herbal-therapy usage. Moreover, we need to talk with our patients about herbal supplements in order to determine current consumption and provide safe and complete health care. It has become obvious over the past few years that clinician approval does not always matter when it comes to patient use of supplements, so communication is crucial.
Ms. Sego is a primary-care nurse practitioner at the Department of Veterans Affairs Medical Center in Kansas City, Mo., and a contributing editor to The Clinical Advisor.
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