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Top Herbal Products: Efficacy and Safety Concerns

  • Authors: Darrell T. Hulisz, PharmD
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Target Audience and Goal Statement

This activity is intended for pharmacists, primary care physicians, nurse practitioners, physician assistants, nurses, and all clinicians caring for patients who are likely to be using herbal remedies.

The goal of this activity is to review traditional uses, evidence-based data, mechanisms of action, side effects, contraindications and herb-drug interactions of the most popular herbal products on the US market.

Upon completion of this activity, participants will be able to:

  1. Describe traditional and evidence-based uses of the most commonly used herbal products
  2. Explain the probable mechanisms of action of these therapies
  3. Discuss side effects, contraindications, and drug interactions of the most commonly used herbal products


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Medscape, LLC encourages Authors to identify investigational products or off-label uses of products regulated by the US Food and Drug Administration, at first mention and where appropriate in the content.


  • Darrell T. Hulisz, PharmD

    Associate Professor, Department of Family Medicine, Case Western Reserve University School of Medicine, University Hospitals, Case Medical Center, Cleveland, Ohio


    Disclosure: Darrell T. Hulisz, PharmD, has disclosed that he has received grants for educational activities from Pfizer, Takeda, and Novartis. Dr. Hulisz has also disclosed that he has served as an advisor or consultant for Pfizer, Takeda, and Novartis.


  • Christine Wiebe, MA

    Editorial Director, Medscape Medical Students and Pharmacists


    Disclosure: Christine Wiebe has disclosed no relevant financial relationships.

  • Jacqueline A. Hart, MD

    Freelance Clinical Editor, Medscape, LLC, Boston, Massachusetts


    Disclosure: Jacqueline A. Hart, MD, has disclosed no relevant financial relationships.

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Top Herbal Products: Efficacy and Safety Concerns


Valerian, Chamomile, Ginger: Calming Agents


Valerian root (Valeriana officinalis) has been used for centuries for its calming effects. Medics gave it to soldiers during World War I for the treatment of shell shock.[87,88] The active ingredients appear to be valepotriates (thought to be responsible for the sedative effects) and valeric acid, both of which mediate the release of gamma-aminobutyric acid. Randomized clinical trials have demonstrated efficacy of valerian root extract for treating insomnia.[89,90]

Mild side effects have included paradoxical stimulation (restlessness and palpitations), especially with long-term use. Valerian should not be used in pregnancy. This herb may have an additive effect with other central nervous system depressants. Patients should be cautioned regarding the operation of machinery when initiating therapy until they are accustomed to the effects. Other potential side effects include headaches, excitability, and uneasiness. Typical dosages for insomnia are 200-400 mg (standardized to 0.8%-1% valeric acids per dose) at bedtime.


Few human studies have been published on the use of chamomile (Matricaria recutita), yet it is cultivated worldwide for its sedating and calming properties. The active component apigenin has been shown to bind the same receptors as benzodiazepines, to exert an anxiolytic and mild sedative effect in mice.[91] Chamomile also has moderate antioxidant, antimicrobial, and antiplatelet activity in vitro.[92]

Chamomile is considered safe by the FDA, but it should be used with caution in individuals who are allergic to ragweed, as cross-allergenicity may occur. Allergic symptoms include tongue thickness, tight sensation in throat, angioedema of lips and eyes, diffuse pruritis, urticaria, and pharyngeal edema.[93,94] Because of its sedative effects, chamomile should be used with caution when taken in conjunction with medications that have also sedative side effects, or with alcohol. Oral doses vary from 400 to 1600 mg per day (standardized to 1.2% apigenin per dose). Chamomile is often brewed as a tea; 1 heaping teaspoon of dried flowers steeped in hot water for 10 minutes may be drunk up to 3 times a day.


Ginger (Zingiber officinale) is cultivated in Asia, Africa, and the Caribbean. It has been used for centuries as a flavoring agent and for its antiemetic properties. The root produces a volatile oil containing shogaol and gingerol.[95] Gingerol and shogaol have demonstrated analgesic, anti-inflammatory, sedative, antipyretic, and antitussive properties in vitro and in animals, as well as antioxidant antimicrobial, antifungal, antineoplastic, and antihypertensive benefits; many of these effects have yet to be tested in people, however.[96] Human studies have shown a significant reduction in nausea in patients with hyperemesis gravidarum taking doses of 250 mg 4 times a day,[96-98] and in patients with perioperative nausea and vomiting taking doses of 1 g prior to surgery.[99,100] A study comparing ginger with 100 mg dimenhydrinate and with placebo found that ginger was superior to both when patients were subjected to a revolving chair designed to produce motion sickness.[101]

Ginger has exhibited inhibition of thromboxane synthetase that resulted in prolonged bleeding.[102] Therefore, it is prudent for those taking anticoagulants to have their International Normalized Ratio (INR) monitored closely. Ginger can also cause mild gastrointestinal (GI) upset including heartburn, diarrhea, and mouth irritation.[96]

Take-home message: Valerian, chamomile, and ginger can be safely recommended in the majority of patients. These agents have shown modest efficacy for their primary uses. However, patients with chronic anxiety and insomnia should be under the care of a healthcare professional and thus should not attempt self-medication with botanicals.

Ginseng: A Natural Energy Booster

The term ginseng (Panax ginseng, Panax quinquefolius) means "man-root," and the ancient Chinese believed it could benefit all aspects of the human body; today, it is mostly used as an energy booster.[103] "Siberian ginseng" is derived from the Eleutherococcus senticosos shrub and has different properties than ginseng from the Panax family[104]; in fact, federal regulation now requires that this product be referred to as eleuthero to distinguish the 2 herbs.[105]

Derived from the root of the plant, the ginsenosides found in ginseng are a compilation of more than 20 saponin triterpenes and are thought to be the active ingredients.[106] Animal studies suggest that these steroid-like compounds work by stimulating the secretion of adrenocorticotropic hormone, resulting in increased production of cortisol.[107] The herb may also play a role in stimulating the production of adrenal hormone precursors.

Ginseng is considered by many to enhance physical, sexual, and mental performance, as well as increase resistance to stress. Because these potential benefits are somewhat subjective, however, controlled clinical trials are difficult to interpret. Generally speaking, results from clinical trials have been equivocal.[103]

Although it is much too early to tell how this may affect people with diabetes, animal studies suggest that ginseng may reduce glucose levels in obese, diabetic mice.[108,109]

Because it can have a mild stimulant effect, it should be avoided by patients with cardiovascular disease who are taking other stimulants. Ginseng has also been associated with reversible mastalgia and postmenopausal bleeding, although this appears to be a rare side effect.[110] Overuse of ginseng may be associated with diarrhea, hypertension, nervousness, dermatologic eruptions, and insomnia. This herb has also been associated with a reduction in the INR of warfarin-treated patients.[111] In addition, ginseng has been associated with altered hemostasis and is therefore contraindicated in patients with active bleeding; patients receiving anticoagulant and/or antiplatelet medications should be cautioned against using ginseng.[112]

As with many other herbs, ginseng formulations have not been standardized, nor have optimal doses been determined, but common regimens involve 100-600 mg per day in divided doses.

Take-home message: Historically, many claims have been made by supporters of Panax ginseng formulations; however, robust clinical trials are lacking. Patients who use ginseng should be cautioned not to exceed the labeled dosage since adverse effects may occur. Clinicians should discourage use in patients who are anticoagulated, and those with cardiovascular or metabolic disease, such as hypertension and diabetes.

Saw Palmetto: Effective for Benign Prostatic Hyperplasia?

The extract for saw palmetto (Serenoa repens) comes from the fruit of the palm tree and is often used to treat benign prostatic hyperplasia (BPH). Saw Palmetto extract is thought to inhibit 5-alpha reductase and thus block the conversion of testosterone to dihydrotestosterone, which is responsible for stimulating growth of the prostate gland.[113] It also blocks the uptake of both hormones by the prostate. Saw palmetto may exhibit some anti-inflammatory effects, presumably by inhibiting cyclooxygenase pathways.[114]

While early clinical studies suggested a modest benefit of saw palmetto in BPH, more recent studies are less consistent, and the precise clinical value of saw palmetto for treating urinary symptoms remains undefined.[115,116] In a recent randomized, double-blind, placebo-controlled trial, 225 men were given either standardized saw palmetto 160 mg twice daily or placebo for 1 year.[116] There was no significant difference between the 2 groups in the change in objective urologic symptom scores, maximal urinary flow rate, prostate size, residual volume after voiding, quality of life, or serum prostate-specific antigen levels. The incidence of side effects was similar in the 2 groups.

Side effects are uncommon with saw palmetto, but they may include headache and GI upset. There are no known important drug interactions with this herb.[113] The most commonly used dose for treating BPH is 160 mg twice daily.

Take-home message: Men with obstructive urinary symptoms should not self-medicate with saw palmetto. Such patients should be under medical supervision, because the symptoms of BPH can mimic other, more serious disorders, such as prostate cancer and prostatitis. This herb should be reserved for men with mild BPH symptoms who have an aversion to prescription drugs and are also under medical care.

Black Cohosh Used to Ease Hot Flashes

Black cohosh (Cimicifuga racemosa) is a plant native to Eastern North America. It contains a group of chemicals referred to as phytoestrogens because they mimic the effects of estrogens. For this reason it was a common remedy used by Native Americans for the treatment of painful menses (known as squawroot).

Recent clinical trials indicate that black cohosh is somewhat efficacious in relieving menopause symptoms.[117-121] The majority of the trials used the isopropranolic extract of black cohosh at a total dose of 40-80 mg daily. Most studies were only conducted for a short duration of either 3 or 6 months. Thus, further clinical trials are needed to assess efficacy of black cohosh beyond 6 months. Recent investigations do not support the earlier estrogen-receptor mediated theory as a plausible mechanism of action of black cohosh including a randomized, placebo-controlled, 1-year study of 351 women with menopausal symptoms failed to confirm efficacy of black cohosh.[122]

Black cohosh is generally considered safe without any major life-threatening adverse events.[121] Some patients may experience mild side effects including rash or GI upset. It should not be used in lactating or pregnant women. Since there is still speculation of an estrogen-like effect, black cohosh use should be avoided in women with a history of estrogen-dependent tumors or endometrial cancer. Most authorities suggest limiting its use to 6 months because no long-term trials have been conducted. Black cohosh offers an alternative to estrogen for symptoms of menopause, the most widely studied dose is 20-40 mg twice daily standardized to 1 mg triterpene glycosides.

Take-home message: Clinical trials using black cohosh to relieve menopausal symptoms have yielded conflicting results. However, some women experience benefits with the herb without apparent side effects. It appears to be safe, but use should be limited to no more than 6 months and should not be used in those with a history of estrogen-dependent tumors.


Consumers with serious or chronic health complaints will often self-diagnose and self-treat with herbs and supplements. This is not ideal, because many of these patients need supervised medical care, especially those with depression, prostate disease, dementia, or chronic insomnia.

Health professionals generally should advise against the use of herbs or supplements during pregnancy or lactation, because the effects on fetal development and breast milk excretion are unknown. Similarly, use in infants and younger children should be discouraged.

Patients should be advised to take the same dosages that have been studied in clinical trials, and not to exceed labeled amounts. Generally, herbs should be consumed only for a limited time. Patients should avoid products with labels that fail to specify the exact amount of the herb contained per dosage unit.

Health professionals should elicit a careful history from patients regarding any plant allergies, especially to ragweed and daisies, recalling that many patients with allergic rhinitis may not know what allergens trigger their attacks. Patients who are allergic to ragweed and flowers in the daisy family (asters, chrysanthemums) may have allergic reactions to products containing echinacea and chamomile. Some herbs are photosensitizing (eg, St. John's wort), and patients should be cautioned appropriately (especially fair-skinned individuals).

Patients anticipating surgical procedures should discontinue use of herbs at least 2 weeks prior to surgery, and should notify the anesthesiologist of any routine herb usage.[54] As discussed, some herbals may interfere with normal blood coagulation, predisposing patients to prolonged bleeding and interactions with warfarin (eg, garlic, ginkgo, ginseng, and ginger).



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