Herbal Medicine: Safety of Herbal Medicine

A major benefit of herbal medicine is its long history of safe use. Humans have been taking herbal medicine for thousands of years. This is like a huge experiment where thousands if not millions of people are utilizing plants to benefit their health and relieve symptoms, in some cases herbs like garlic have at least 3,000 years of safe use. Contrast this with many pharmaceuticals that have only a few years of studies and human use to support their safety. As it turns out, about 5% of drugs have to be pulled from the market after some years of use.

In many cultures herbal medicines are added to food, and taken daily as tonics and restorative remedies. In European studies comparing herb preparations and pharmaceutical drugs, the side effects of the herbal remedies when compared with pharmaceutical drugs is typically one half, or equivalent to the rate of side effects for the placebo.

As recently as the early 1980s, doctors, regulators, and even the news media were not much interested in the concept of herb safety. Why? Because most didn’t believe herbs had any effect at all, much less pose a public safety threat.

This all changed in the mid-1990s with the rise in popularity of St. John’s wort, kava, ginkgo, and other top herbs. Enough high-quality studies were finally available to convince many skeptics that herbs in fact did have activity. Subsequent studies have shown that herbs have in some cases as much activity as pharmaceutical drugs. Since then, several factors have combined to bring herb safety to the forefront.

  • In clinical trials, mostly from Europe, herbal products have shown similar activity to pharmaceutical drugs for relieving symptoms such as depression and anxiety.
  • Modern herbal products can be highly concentrated. Some of the active constituents might be purified and then added back into extracts at up to 95% of the total! This high concentration makes the preparations that contain these extract more like drugs than herbs, at least in the traditional sense, and while these concentrations might increase the efficacy of the products in some cases, it also increases the risk of side effects and herb-drug interactions.
  • The herb ephedra (ma huang), a traditional Chinese herb that contains substantial amounts of the alkaloid ephedrine became national news when it was linked to a number of adverse events and even deaths in the U.S.
  • Many more people today are taking prescription drugs and herbs together—as many as 25 million people in the U.S. alone.

Herbal Safety—How Safe Are They?

Despite a huge upswing in the popularity and use of more concentrated herbal medicines world-wide, it is not easy to come up with any statistics or studies that show that herbs are not safe when taken as generally recommended today on product labels, and doses given in popular herb books.

The World Health Organization created one of the largest herb safety databases in the world. A thorough search of this database shows that very serious side effects or interactions have been reported internationally over the last xx years. [Give example from Artemisia search].

Very few reports of serious adverse events associated with herbal medicines can be found after a thorough search of databases and reports from government agencies such as the centers for disease control (CDC), and the food and drug administration (FDA), charged with monitoring the safety of the drugs and devices used in health care.

A search of Toxline, one of the major sources of information on toxic substances, maintained by the National Library of Health, as part of the largest medical database in the world, PubMed, shows that herbs are inherently safe, with a few caveats:

  • After reviewing numerous clinical trials with a total of thousands of patient volunteers, the most common side effect from taking herbs are digestive upset and headaches. These quickly resolve after reducing the dose or discontinuing the herbs.
  • Herbs used in their whole form are usually safer than when used in highly refined forms.
  • Some people are allergic to or react adversely to herbs that most people can use safely.
  • People who have life-threatening diseases (particularly heart disease and liver disease) and are taking several to many prescription drugs should use caution when taking herbs. It is best to consult with professional health care providers such as licensed acupuncturists and professional herbalists, in concert with your physician.

Herb-related adverse effects usually fall into the categories contraindications, side effects, and interactions.


Most traditional systems of medicine, especially traditional Chinese medicine have defined conditions where specific herbs should not be taken. For instance when the patient has digestive weakness, or when they are taking other specific herbs. These potential interactions are not considered dangerous, but not following these contraindications could negate the positive effect of the treatment, or even lead to worsening of the condition or symptoms.

Side Effects

Herbs generally can cause either digestive upset or allergic reactions. Digestive upset can result from taking some herbs like ginkgo standardized extract, especially on an empty stomach. In their whole form, herbs have lots of crude fiber, and can be tough to digest for some people. Herb extracts are often easier to digest and usually cause less digestive upset, though even extracts can cause a feeling of nausea or fullness to occur in some cases. The possibility of digestive upset can be counteracted and the absorption enhanced by adding some spicy herbs like ginger to the formula, or taking the herbs with ginger tea. Using an herbal formula that is skillfully formulated by an experienced herbalist can reduce the possibility of side effects and increase the effectiveness because these factors are considered ahead of time. At home, add a little ginger, cinnamon, and other favorite spices to your herb teas to enhance the enjoyment and reduce digestive upset.

Severe side effects of herbal preparations are unusual, when used as recommended on the product, but a few are best taken under the advice of an experience herbal practitioner because of reports of possible toxicity. Please consult the [Herbal Database] for specific information on 245 herbs.

Herbs with Potential for Side Effects or Toxicity

Herb Use Potential Side Effects or Toxicity
Blue Cohosh
(don’t use during pregnancy)
Usually with black cohosh just before birth to stimulate contractions, but also in some “women’s formulas.” Potentially toxic to the heart of the fetus, has other toxic compounds
(Not for long-term use or excessive doses internally.)
Traditional remedy for colds, flu, infections, cancer, and more. Liver toxicity reported in the literature without much evidence.
(Not for long-term use or during pregnancy internally.)
Healing application for burns, cuts, skin trauma. Liver toxicity reported in the literature with only moderate support.
(Generally safe. Consult your health care professional if you have pre-existing liver disease. Caution using with alcoholic beverages or other sedative pharmaceuticals like benzodiazepines.)
Traditional social drink in Pacific Islands. Used today for muscle tension, anxiety, nervousness, insomnia. Liver toxicity reported in the literature on some preparations containing stem extracts. For traditional root and rhizome extracts, moderate concentrations (below 20% kavalactones, teas, and tinctures less likely to cause problems.
Any liver toxicity is likely to be due to rare allergic reactions.
(Use in small amounts in formulas mostly safe.)
Antispasmodic for asthma, also used in stop-smoking mixtures Can cause nausea in even moderate doses, but not considered dangerous by herbalists.
(Internal use of the tea in moderate amounts is likely to be safe. Don’t use during pregnancy.)
Used for digestive problems, poor digestion, flatulence, to stimulate menses. Contains the potentially toxic compound thujone. Preparations made with alcohol should not be used more than a few days once in awhile. Teas contain very little thujone.
(External use mainly, except under advice of an experienced herbalist.)
Used in cancer treatment protocols externally and internally. Also for lymphatic congestion and swellings, and venomous bites. Can definitely cause nausea and vomiting in even small amounts when used internally. I recommend internal use under guidance of an herbalist.
(The use internally in tea form for short periods is likely to be safe.)
Used in spring tonic teas and formerly to flavor root beer. Some animal studies show one of its constituents, safrole, to be a potential carcinogen and mutagen. Very little safrole in teas.
Scullcap Used as a general nervine or nerve tonic or relaxing herb. Sometimes as an antispasmodic. Scullcap itself is not considered toxic, but it is commonly adulterated in commercial products with the potentially liver-toxic herb germander. Fortunately, this adulteration is very un- likely with organically-grown herb.
Wormwood Used for digestive problems, poor digestion, flatulence, to stimulate menses. Also as a worm remedy. Contains the potentially toxic compound thujone. Preparations made with alcohol should not be used more than a few days once in awhile. Teas contain very little thujone.


Now that millions of people around the world are using herbs and pharmaceutical drugs together as part of their daily regime, interactions are certainly possible in some cases. Interactions can happen because herbs contain complex mixtures of many active compounds, and some of them have the potential to change the way pharmaceutical drugs are absorbed, metabolized, distributed throughout the body, and eliminated.

The major site of this potential interaction might be the liver. When you swallow a drug, the chemical compound is affected by enzyme systems in the liver in some way. It is often altered, and can be changed to compounds that are more easily eliminated by the body, as is necessary with all potentially toxic compounds.

Some common herbs, most notably, St. John’s wort, has been shown by human studies to lower the concentrations of common drugs in the blood system. When these drugs are potentially life-sparing, like the anti-rejection drugs taken after organ transplants, antiviral drugs (for HIV infections), or chemotherapeutic drugs used in the treatment of cancer, then a problem could occur.

Herbalists often recommend that if you are in poor health and taking pharmaceutical drugs, especially if they are potentially life-sparing like blood-thinners, then consult with your physician and your herbalist or other natural health care practitioner before taking any but the Safe 10 herbs in Table xx.

Despite a few documented cases of herb-drug interactions, it is remarkable that with 25 million people in the U.S. alone taking herbs and drugs together, as is estimated, so few actual clinical reports of interactions have been published in the scientific literature. This seems to indicate that herb-drug interactions are not a very important public health safety problem.

Nevertheless, we are learning more about the actions of herbs, and the pharmacology of their major active compounds is becoming increasingly known. Because of this new knowledge, many books and articles on herb-drug interactions do make theoretical statements about interactions. Hopefully, these sources will make sure to state whether an interaction they list is theoretical or actually reported in humans. Studies on interactions using animals are not very reliable because each animal species metabolizes herbs and drugs differently.

Herbs Suggested to Increase Bleeding

Caution with Anti-Clotting Drugs like Warfarin which can Increase Bleeding

  • Ginkgo
  • Ginger
  • Garlic
  • Red Chinese Sage
  • Feverfew

Other Theoretical or Potential Interactions

  • Ginseng: may reduce effectiveness of some anti-clotting drugs
  • Caution is recommended with all of these herbs for 1-2 weeks before and after major surgery because of the theoretical potential to prolong bleeding time
  • St. John’s wort may reduce blood levels of certain drugs like warfarin, antiretroviral drugs, or anti-rejection drugs
  • Licorice can possibly potentiate the potassium-releasing effect of pharmaceutical diuretics like Lasix

Note: this list is not exhaustive, but presents some of the better-known theoretical and potential herb-drug interactions. For more complete information on herb safety and herb-drug interactions, see Mills and Bone (2005).

Safe 10 Herbs

While anyone can experience mild allergic reactions to an herb or herbal preparation, or even extremely rare life-threatening allergic reactions, these 10 herbs are very unlikely to interact with drugs that you are taking. These herbs are all generally considered safe to take during pregnancy as well.

  • Chamomile—a good-tasting tea to drink throughout the day, or as needed, for mild nervousness, and many digestive upsets such as intestinal cramps, mild nausea, or a feeling of general digestive discomfort. Chamomile is also used for relieving menstrual cramps and pain.
  • Nettle leaf—a popular mineral tonic to take during pregnancy, or anytime. Reported to help “build the blood,” and also help maintain good urinary tract health.
  • Lemon balm—safe for infants and young children. A mild calming tea to give during teething, digestive upset and colic. Administer 1-3 droppers full of the mild, good-tasting tea. Good for teenagers and adults too by the cup.
  • Elder berry, elder flower—a great herb to help lower fevers, and it has antiviral effects, being one of the best-studied herbal remedy to help counteract flu.
  • Andrographis—another well-studied anti-flu herb.
  • Peppermint—makes a good-tasting tea for relieving digestive pain due to gas, upset stomach, and nausea.
  • Linden—a great-tasting tea for relieving mild nervousness and sleep disturbances.
  • Echinacea leaf and flower—a classic traditional herbal remedy to shorten symptoms of colds and flu, and other kinds of infections. Some scientific studies show that children get fewer colds during the winter season when using the herb regularly, off and on.
  • Hawthorn—A famous heart “tonic.” Some human studies show beneficial effects for people with mild heart weakness, and hypertension. Herbalists respect the herb for the herb’s strengthening effect on the heart.
  • Shiitake—one of the best-studied immune tonics, used in traditional Chinese cooking for thousands of years. Today, it is known to have antiviral and anticarcinogenic effects.

Herb Effectiveness

Efficacy of Herbal Medicine

You may be surprised to know that today many herbal medicines have substantial scientific evidence demonstrating their safety and efficacy. The news media sometimes reports on negative studies or safety issues involving herbs, but rarely reports on the successes or the long safety record that stands behind many herbal remedies. In Europe, herbal medicine takes a more scientific path, relying on extensive scientific investigation, testing, and clinical trials before it can be licensed for sale to consumers or patients.

Few would say that herbal medicine is inherently dangerous, or a public health and safety concern, yet how effective is herbal medicine? Citing European clinical trials involving as many as 10,000 to 20,000 people, one generally finds that herbal medicine is equally effective for relieving symptoms of a number of common ailments than the equivalent pharmaceutical drug. This is especially true when one considers some of the best-known and most widely used herbal remedies. These include ginkgo (for dementia), St. John's wort (depression), saw Palmetto (prostate hyperplasia), Elderberry (flu), garlic (blood cholesterol), and kava (mild to moderate anxiety). A major question that has to be asked is if some herbal medicines have strong scientific support for efficacy and safety, are turning out to be as effective as pharmaceutical drugs in some human trials, at one quarter of the cost in half the safety problems, then why aren't they more commonly recommended by physicians and included on hospital formularies? We might suspect that the answer to this is obvious, political and economic. It is also likely to be due in part to the human beings resistance to change and new ways of doing things. Today there is getting to be enough solid science, economic and environmental reasons to choose herbal medicine over pharmaceutical drugs, especially as the first line of treatment. Why start off with something that is likely to be less safe, more expensive, harder on the environment and possibly our body, yet have no proof that it is any more effective?

If you are looking for herbs with positive human studies, start with this list of ten top herbs.

Top 10 Herbs With Double-Blind, Placebo-Controlled Studies

  • Black Cohosh
  • Echinacea
  • Elderberry
  • Garlic
  • Ginger
  • Ginkgo
  • Ginseng
  • Kava
  • St. John’s Wort
  • Saw Palmetto


Mills, S. and K. Bone. 2005. The Essential Guide to Herbal Safety. London: Churchill Livingstone.

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