Herbal Actions and Interactions

Guidelines for Safe Use of Herbs

“Only two things are infinite, the universe and human stupidity, and I’m not sure about the former. ”
– Albert Einstein –

Q. I have read warnings in well-respected publications that herbal medicines can pose serious dangers. How concerned should I be?

A. This question was answered very clearly by Jim Duke, Ph.D., former head of the USDA botanical division, author of numerous best-selling books on herbal medicine, and one of the most generous of herbalists in sharing his knowledge. On one of his many web sites he published a list comparing with other common causes of death your chances of dying from the use of herbs or dietary supplements.

Dr Duke’s Herbal “Chance of Dying from” Death List
(from safest to least safe)

Herbs: 1 in 1,000,000
Supplements: 1 in 1,000,000
Mushrooms: 1 in 100,000
Food poisoning: 1 in 25,000
NSAIDS: 1 in 10,000
Murder: 1 in 10,000
Hospital surgery: 1 in 10,000
Car accident: 1 in 5,000
Improper use of medication: 1 in 2,000
Angiogram: 1 in 1,000
Alcohol: 1 in 500
Cigarettes: 1 in 500
Western medicines: 1 in 333
Medical mishap: 1 in 250
Iatrogenic hospital infection: 1 in 80
Bypass surgery: 1 in 20

Putting things in Perspective

Every year hundreds of thousands of people die from prescription drug reactions Reading this reports makes it very clear that, by comparison, the chance of being killed by herbs is pretty small. In fact, you would probably have to be pretty unlucky to kill or harm yourself with herbs, though it is not impossible. My favorite anecdote about an herbal death won the first place Darwin Award a few years ago. The Darwin Award, bestowed over the Internet, is given to the person who dies in the dumbest manner. In this particular case, an Italian zookeeper had a constipated elephant. He decided to give the poor beast a laxative (senna or castor oil-based, no doubt), and happened to walk behind the distressed pachyderm at the most inopportune moment. Drowning was listed as the official cause of death.

Okay, so herbs are not likely to kill me. Will they cause serious injury?

Mark Blumenthal, director of the American Botanical Council and editor of HerbalGram, wrote an article in 1991 in which he cited emergency room and poison control center statistics. The findings illustrated that at that time, the true incidence of reported injury by herbs was so low that there was no official category.

Of course there are cases which are not reported, and undoubtedly anything including herbs can cause serious problems. If we modify this to estimate that herbs seriously injure a few hundred people every year, we can see how it compares to other forms of injury. Mark cited an Associated Press article stating that in 1991, 580,000 people were injured on bicycles, 82,000 on skateboards, and 98,000 on roller skates, while 33,000 people were injured in accidents involving shopping carts!

I’m still not convinced.

Good, because there are two more things that need to be made clear. First, herbs contain chemicals, and though generally safe, can cause severe allergic reactions and even death, just like foods. Most but not all of these reactions are preventable if you educate yourself, as you are now doing.

Second, you must take responsibility for your own health. This means you must take the time to learn to listen to your own body, find good sources of information and check with your physician before you change or stop any prescription medicines you are taking. Make sure that all your caregivers know exactly what you are doing. I am always very impressed when new patients show up with clearly written lists describing all the medications, prescription or natural, that they are taking. Dr. Duke tells me that his HMO doesn’t even want to hear about the herbs he takes-which is all he took in 1998 except for seven Aleve tablets-so you must be sure to inform your doctors about any herbs you are taking.

Allergic and Hypersensitivity Reactions to Herbs

It is possible to have an allergic or hypersensitive response to almost any substance. In practice, certain herbs are more likely than others to cause allergic reactions. I estimate that in my practice one patient in a thousand experiences an unexpected allergic reaction. So far, all except one have recovered within 24 hours, simply by stopping the herbs. (The remaining case required steroids to relieve the itching caused by a reaction to the herbs.)

There was no pattern at all to these events, so I think it is impossible to predict such reactions in advance. The mild level of the reactions compared to, say, a bee sting, is probably because the concentration of allergens is relatively low in most herbs consumed orally. It is equally probable that an allergic response might occur as a result of exposure to an unexpected contaminant in the preparation, rather than the herb itself.

Here is a short list of medicinal plants related to ragweed, from the Aster plant family, which might evoke allergic responses in some people. Unfortunately the Aster herbs and shrubs are arguably the largest family of flowering plants, comprising about 1,100 genera and 20,000 species. Interestingly, some of the plants from this family are used to treat allergies. Dr. Duke’s database also lists individual phytochemicals that have been reported to be allergenic.

Arnica flowers (Arnica montana)
Artichoke leaves (Cynara scolymus)
Boneset (Eupatorium perfoliatum)
Burdock (Arctium lappa)
Camomile, German (Matricaria chamomilla)
Chicory (Cichorium species)
Dandelion root/leaves (Taraxacum officinale)
Echinacea (Echinacea species)
Feverfew (Tanacetum parthenium)
Goldenrod flowers (Solidago species)
Wormwood (Artremisia absinthium)
Yarrow leaves/flowers (Achillea millefolium)
Zi wan root (Aster tataricus)

If you suspect you are having an allergic reaction to an herb or herbal preparation, stop taking it immediately and call your health care practitioner.

Hypersensitivity is a more common problem, affecting perhaps 1% of people who take herbal medicines. These are unexpected reactions of various sorts that other people do not have. Symptoms may develop such as elevated liver enzymes, nervousness, changes in blood pressure, fatigue etc. If such responses occur, they are unpredictable, and patients should always discontinue the herbs and consult with their doctors.

Allergic and hypersensitive responses to herbs sometimes indicate imbalances in the intestinal flora. People suffering from intestinal dysbiosis or chronic intestinal infections will often find themselves becoming increasingly allergic to more and more things, including the herbs that are supposed to help them. The reasons for this are complex, but I agree with the Naturopathic explanation that chronic intestinal inflammation leads to an increase in permeability across the intestinal membranes, allowing larger molecules to pass through, triggering immune response

Digestive Problems with Herbs

Digestive problems, however, are very common with herbs. which makes sense, as they are basically very concentrated vegetables, often 10 or 20 times as concentrated as foods. As a result, nausea, loose stools and acid reflux can occur.

This can scare new patients away from treatment if it occurs, so I take it seriously. I tell them to imagine if they were to eat their favorite food, a food that causes no problems with digestion , but would cause nausea and vomiting and diarrhea if they ate 10 times too much, say 10 Italian meals. Does that mean there is something wrong with the food, or is it just too much for the stomach?

Often these problems are transient and can be fixed with dosage adjustment or addition of digestive aides like ginger, digestive enzymes or apple cider vinegar.

Rules to Follow when Using Herbs

As safe as herbs are in general, here are some rules to make you even safer.

• Consult with someone who is properly trained before using herbs to treat a medical condition

• Consult with your doctor or herbalist if you are also taking Western prescription medications.

• Always read labels carefully.

• Read about an herb in at least two different sources before taking it.

• Don’t believe claims about miraculous cures.

• Follow dosage recommendations. More is not always better. Start with moderate doses and increase over time if necessary.

• Heed contraindications, which are there for your safety. Note that contraindications are often understated in clinical settings and on written instructions, so you may have to do some of your own research.

• Monitor yourself for reactions, and discontinue herbs if you notice any adverse effects.

• If you have a serious reaction to an herb, call 911.

Drug Interactions

Can I take herbs along with the other medicines given to me by my doctor?

This is perhaps the most common question people ask me. Historically, herbs and pharmaceutical drugs have been developed independently, and only in the past 40 years has there been widespread concurrent use of these two forms of medicines. It is now very common for patients to consult more than one allopathic doctor, and for patients to turn to herbalists for information and take supplements purchased at health and nutrition stores. Many people are taking multiple drugs, herbs and vitamins at the same time. It is very difficult to predict in advance any side effects that may occur as a result of such combinations, yet it is unreasonable to ask people to just give up potential solutions to their health problems. Skilled observers are now saying that it is important to learn and report as much as we can about drug-herb combinations (Chen, 1999). In our clinic, we often prescribe herbs side by side with Western medications, and we see few problems. When problems do occur, they are invariably quickly resolved. Nonetheless, we should pay close attention to certain areas where interactions are likely, such as with cardiac medications.

Believing that herbs are categorically safe or unsafe is insufficient. While it is true that herbs may harm only one person in a thousand, and only kill one in a million, it is my job as a professional herbalist to make sure you are not that one. In the rest of this section we will review every major concern with regard to herbal medicine toxicity of which I am currently aware. By the end you will hopefully know more than enough to protect yourself. I will provide lists of herbs for which there may be some concerns in each section. However, these lists are not exhaustive. For more exhaustive coverage, I suggest you get a copy of the Botanical Safety Handbook, the PDR for Herbal Medicines or vist the British Herbal Safety News website.

In a later part of this section you will see a listing of some very dangerous plants (Herbs that Kill), even though it is unlikely you will ever be able to buy them. This is to instill in you a little bit of respect for the power of plants. Remember, even though poisoning or death by herbal medicines is very rare, it is still possible.

Potentiation and Inhibition of Medication Efficacy – Quick Summary

Herbs can increase or decrease your absorption of nutrients and Western medications. Being aware of this possibility will help you to spot such a problem if it occurs. This can be a critically important consideration if you are taking medicines that have a high danger potential, such as cardiac glycosides (heart medications) and blood-thinning agents.

Some herbs contain large amounts of mucilage and other types of fiber, and therefore may inhibit absorption of certain medications. Bulk-forming laxatives are the most common category of herbs to do this.

Herbs that strengthen digestion and absorption may increase absorption of medications. This alone may account for the reason so many persons have reported being able to reduce their medications after taking herbs. Both cayenne and black peppers have shown to speed up absorption of various chemicals including phytochemicals.

It is also known that many herbs can change the way the body processes and eliminates drugs in the liver. Many herbs and common foods have effects on liver enzyme systems, and can change blood levels of drugs. St. John’s wort was implicated in January of 2000 in lowering the blood levels of AIDS drugs and cyclosporine, a drug used to prevent organ rejection. In both of these cases, the results could be deadly (Piscitelli et al., 2000).

A special case of potentiation is seen with grapefruit juice. It contains a compound called bergamottin, which inactivates cytochrome P450-3A4, a digestive enzyme that metabolizes up to 60 percent of all drugs, including anti-histamines, statin drugs for cholesterol and various high blood pressure medicines. This may explain why grapefruit juice potentiates the effects of many prescription drugs. When ingested with grapefruit juice, blood levels of some drugs can reach five times their normal levels, which is especially dangerous with cardiac glycosides (Eagling et al., 1999, He et al., 1998).

In the above cases, concerns are limited to people taking drugs where lowering below therapeutic levels is dangerous. In you are not taking such medicines you certainly can drink grapefruit juice. Otherwise, consult a trained practitioner.

Blood Thinners

Many herbs contain mild to moderate blood thinning or thickening properties. For example, foods and herbs containing Vitamin K (which allows the body to produce proteins that clot blood) are widely distributed in nature. Because the actions by themselves are not strong, and because there are many steps in the pathway of coagulation, they almost never pose a danger. Nonetheless, strong blood-thinning and catalyzing herbs should be avoided if you are undergoing surgery, along with supplements like vitamin E. If you are taking a blood thinner such as Coumadin (Warfarin), you must exercise caution both when taking herbs that may further thin your blood or when consuming foods which contain Vitamin K. If your blood clotting time changes too much, you could be in danger of hemorrhage or increased risk of stroke. Here is a list of food sources and their content of Vitamin K, which may potentially counteract blood-thinning medications if used in excess.

Foods high in Vitamin K – (Booth and Suttie 1998)

• Kale – 6.18 parts per million
• Parsley 5.48
• Spinach – 3.80
• Cabbage – green – 3.39
• Watercress – 3.15
• Broccoli – 1.79
• Soybean oil – 1.73
• Brussels sprouts – 1.47
• Rapeseed oil – – 1.29
• Mustard greens – 0.88

As far as herbs are concerned, even if you are taking the herbs under professional guidance, the best way to deal with this situation is to have your doctor conduct clotting time studies (prothrombrin or PT time) which determine how fast your blood clots. This should be done about once a week for the first month you are taking the herbs. If the clotting time does not change significantly within the first few weeks, then it is safe for you to continue taking the herb. However, if the clotting time changes by more than a few seconds, you must discontinue the herb or ask your doctor to adjust the dosage of your blood-thinning medication. Be sure to talk to your doctor about this when you discontinue or re-start any herb with significant blood-thinning actions. The use of herbs that strengthen blood vessels, such as berries and tien chi root (Panax notoginseng), can help prevent problems.

Blood Pressure Medications

Some herbs may lower or raise blood pressure. The effects of most blood pressure changing herbs commonly available without prescription are minor. Clinically, I have seen several cases where patients taking herbs were able to reduce their Western prescriptions to avoid side effects by using lifestyle and dietary changes along with mild herbs that reduce blood vessel inflammation. If you are taking blood pressure medications along with herbs it is wise to check your blood pressure regularly, and if any significant changes occur, talk with your physician to see if your medication dosage needs to be modified. The only herbs I have seen actually raise patients’ blood pressure to any significant degree, and this rarely occurs, are astragalus root, yohimbe (Corynanthe yohimbe), and ginseng root. Commonly known herbs that lower blood pressure include linden flowers, mistletoe, rauwolfia root and garlic. For a complete list of herbs that affect blood pressure, refer to Appendix A.

Overuse or Misuse of Diuretic Herbs

If overused, strongly diuretic herbs may dehydrate the body or cause loss of potassium or other essential electrolytes. Dehydration itself can be a cause of inflammation, so I advise you to exercise caution if using these herbs long term. These herbs can also cause or worsen constipation by removing fluids from the intestines. TAM doctors warn that overuse of diuretics can weaken the kidneys. You must be especially careful if using these herbs along with commonly prescribed diuretic drugs (known as thazide diuretics). Mild diuretics in herbal formulas are generally safe. Whenever taking diuretics make sure to include a simple multi-mineral and mineral rich foods to ensure you do not deplete minerals through the urine. A list of diuretic herbs is found in the appendix.

Digestive Problems Caused by Herbs

Some herbs can cause nausea, abdominal discomfort or burning, and diarrhea. This is especially true if they are taken in medicinal doses. Why does this happen? For the digestive system to function properly, the digestive fires should be regular in both amount and activity. Ayurvedic doctors tell us that anyone who digests food properly enjoys good health and plentiful energy. These people have a good appetite in the morning and evening when the stomach is empty; they experience regularity in peristaltic motion and defecation; there is a balance between the stomach and the intestine in which the acid and alkaline reactions act in harmony. A physician can diagnose problems in the digestive system simply through observation of these basic functions.

To maintain a strong digestive system it is very important to follow a regular schedule for breakfast, lunch and dinner, eating the appropriate amounts and varieties of healthy foods. The body naturally maintains its digestive strength when meals are regular. For example, if we always eat lunch at noon, the body will increase the secretion of digestive enzymes at that time.

This phenomenon is easy to identify in people who have developed the unhealthy habit of eating a meal right before bed, and therefore always feel hungry at bedtime. If they force themselves not to eat at that time for a few weeks, they will find that this bedtime hunger disappears. Overeating or not eating at all when the stomach is empty will also damage the digestive fire. In addition, large quantities of meats, sweets, greasy foods and milk products are damaging to the fire, especially if eaten when the stomach is already full.

Diarrhea can sometimes be caused by poor or incomplete digestion. When the body detects a foreign substance beyond its digestive capacity, such as bitter herbs that have been ingested suddenly, it simply decides to let go of the substance as a defensive reaction. Medicinal herbs, by definition, contain large quantities of various strong-tasting components. These preparations are essentially highly concentrated vegetables. If the digestive system is overly sensitive or weak, the strong tastes are likely to upset the stomach, causing nausea or diarrhea. The simplest way to overcome this problem is to reduce the dosage until it matches your digestive capacity. Alternatively, drink some ginger tea, a reliable anti-nausea agent, or add some digestive strengthening herbs or digestive ezyems. This often solves the problem.

If digestive problems continue, you need to identify the cause of the problem and correct it. We will examine digestion in more detail in a later section.

Herbs That Modify Thyroid Function

Goitrogens are substances that may block utilization of thyroid hormone and induce goiter formation. They include a wide variety of substances found in food and water, including industrial waste (Lindsey et al 1992). Persons who have a history of goiter or diminished thyroid function, or are taking thyroid medications, may need to be careful with some of these herbs and foods. The cooking process is thought to inactivate many of the vegetable goitrogens, such as cabbage family plants, so only raw forms of these foods need to be avoided (Murray, 1991). There are some herbs that affect thyroid function through a variety of mechanisms, and they can be used to treat thyroid disorders when prescribed by a qualified practitioner. These plants may raise, lower or regulate thyroid function. For a complete list, refer to the Appendix.

Common food sources that cause goiter:

Members of the cabbage family (Brassica species) including cabbage, turnip, rutabaga and kale.
Cassava root (Manihot species), millet, peanuts, pine nuts and raw soybeans
Milk from cows that have eaten goitrogens
Dietary excess of calcium or fluorine
High levels of indigestible crude fiber, which may bind the thyroxin secreted in the bile and prevent its reabsorption (Ensminger et. al, 1995).

Herbs That Affect Blood Sugar

Many herbs have blood sugar-lowering effects. You can find a complete list in the Appendix. Some of the herbs listed here are based upon traditional usage for diabetes, some upon animal experiments documenting blood sugar-lowering effects, and some upon experiments done with humans. The list is not complete, and there are likely hundreds of other plants that can mildly drop blood sugar.

Although these effects are often mild, they may cause problems for some hypoglycemics or diabetics. I have rarely seen this occur in practice, but it is also true that many people cannot identify the signs of low blood sugar, which include weakness, shakiness, dizziness, a drop in blood pressure, and sometimes ravenous hunger. The only three substances I have seen strongly affect blood sugars unexpectedly in our clinic are chromium picolinate, ginseng root, and gymnema leaves (Gymnema sylvestre). I suggest you monitor your blood sugars carefully if you are taking any of these herbs. .

Herbs that raise blood sugar when used in therapeutic dosage are much rarer, though any sugar or carbohydrate-containing fruit or plant will raise blood sugar if enough is consumed.

Yet More Problems to Know About

Essential/Volatile Oils

Essential or volatile oils are complex concentrated chemicals distilled from plants. There is an entire field of herbal medicine, called aromatherapy, concerning the use of these oils. One drop of essential oil often requires one ounce of plant to produce it. It takes more than 60,000 rose petals to produce one ounce of rose oil. Due to their range of strong scents, perfume manufacturers have studied these oils extensively. Chemically, they tend to be mixtures of oxygenated hydrocarbons, their polymers, and alcohols. A volatile oil from a specific plant will be a blend of a whole range of chemical components. In addition to producing strong odors, these oils are highly antiseptic and anti-fungal, and can even be used as insect repellents. These oils can really burn your skin if you are not careful. Never apply them or even touch them undiluted.

Handle the oils carefully if you decide to use them externally. Wash your hands after each use, and avoid eye contact. I do not recommend using the oils internally unless prescribed by a competent herbalist. If you take too much or use a preparation that is too concentrated, it can cause intestinal inflammation, kidney inflammation, and even kidney infection.

I got a call from a woman who had developed severely itchy hives and wanted to know if she could avoid steroids and use herbs to control the problem. I questioned her about her habits, and found out that a multi-level marketer had convinced her that taking 25 drops of pure eucalyptus oil in water every day would cure her chronic toenail infections. She did this for two weeks before her skin developed the color and texture of lobster claws.

Using Herbs while Pregnant or Breast-Feeding

Using herbs when pregnant or breast-feeding is a serious subject. In the early stages of pregnancy, the fetus is highly susceptible to even minute amounts of chemicals. The cells of the newly formed miracle are changing rapidly, and are thus open to many influences including enzymes, oxidative chemicals, and the like. Anything that influences cell division or fetal circulation can be problematic. Indiscriminate use of foreign substances such as coffee, alcohol, pills or herbs is just plain irresponsible. It is absolutely necessary to exercise extreme caution and consult professionals in these instances.

I do not recommend using herbs while pregnant, unless under the direction of a trained professional. The nutrition that comes from using a good prenatal multi-vitamin is usually sufficient supplementation. TCM doctors, Naturopaths and other herbal professionals are trained to prescribe some simple herbs during pregnancy for problems like morning sickness.

Personally I like the TAM philosophy concerning pregnancy. In Ayurveda, they prefer that women and men prepare themselves for pregnancy prior to conception by using herbs and meditation practices to purify the system. Prayer and fasting are part of these practices in Indian and Nepal, but the basic idea could be modified according your own beliefs. If this is done, hopefully there will be less need for medicine during pregnancy. I discuss this more later.

Breast-feeding is another concern. Strong herbs may pass through the breast milk. This can be good when using gold standard herbs. TAM doctors, for example, say that small amounts of common bitter herbs such as turmeric root are good for purifying the breast milk. Other sources suggest avoiding herbs containing strong alkaloids. I have compiled a list of herbs, gathered from several authoritative sources, to avoid during pregnancy or breast-feeding. Many of these, such as turmeric, are not necessarily dangerous to use, but I see absolutely no reason to take any chances, so I have listed them all. Again, these lists cannot be totally exhaustive. Many of the herbs are listed based upon theoretical concerns. For example rosemary contains volatile oils, but probably would only be problematic if taken in high doses. Herbs that contain phytoestrogens are included, but theoretical concerns have not been proven. Some of the terogenic research is done on animals, and at high doses. Remember, dosage is everything in toxicololgy. As time goes by, safety testing will not doubt show that some of the herbs on this list are indeed safe to use.

I do not want to put pregnant women with health problems in the unfortunate position of having to choose between herbal medicines, which have not undergone safety studies, and Western prescription medicines, which have undergone such studies, but which may potentially be more difficult for the body to handle. Therefore, again, pregnancy is a time when it is very important to consult with a skilled professional herbalist, holistic physician or naturopath trained in the use of herbs. Also, I fully expect that as knowledge in this field improves, we will rediscover ancient methods, and also find new ways to use herbal medicines to benefit unborn children. See the resource guide to find a qualified herbalist. Also, refer to the Appendix for a comprehensive list of herbs to avoid during pregnancy and breast-feeding.

Herbs That Kill

Some herbs are very toxic in their natural state and should never be used. It is best to know something about these herbs to protect yourself by avoiding them completely.

Others dangerous herbs must be purified (neutralized) before they can be used. Aconite species plants contain deadly poisonous alkaloids, and are used medicinally only in purified form. One alkaloid called aconitine is extraordinarily poisonous. Ayurvedic doctors neutralize Aconite poisons in aconite by steaming in cow’s or goat’s milk for three hours and restricting dosage to 1/40th gram (fatal dosage is only 1-2 grams). Chinese doctors neutralize these same poisons by various means, such as soaking the herb in salt, then boiling it with licorice root and black soybeans. These alkaloids initially stimulate your system, then cause paralysis in the motor and sensory nerve endings, as well as the CNS. Intestinal absorption of the alkaloids is rapid, so gastric lavage is recommended in overdose. Keep the patient warm and go immediately to the emergency room.

You might be surprised to learn that ginkgo leaf is toxic until ginkgolic acids are removed.

Certain herbs used commonly in the past are now known to be pretty poisonous and are no longer available except to professionals. Belladonna (Atropa belladonna), for example, was once used in Europe and North Africa to dilate the pupils because they thought this would increase beauty. Excess use causes a blocking of the autonomic nervous system, dry eyes, rapid heartbeat and even stupor and coma. Of course you can’t find capsules of belladonna or deathcap toadstool in your health food store.

Some herbs should be avoided because they can be toxic to the liver, especially those with a high alkaloid content (for a complete listing of these herbs, refer to Appendix A). Comfrey root (Symphytum officinalis) and coltsfoot flower (Tussilago farfara) contain substances called pyrrolizidine alkaloids (PA’s) that can definitely cause obstructive liver damage. They have been shown to cause veno-occlusive disease, endothelial cell glutathione depletion, central vein necrosis, thrombosis, and fibrosis, all very serious conditions (Detlef et. al, 1999). It is probably safe to consider these herbs for short-term internal use under expert medical guidance in certain cases, but long-term used should be avoided.

There is currently controversy over whether the use of the PA containing herbs for short periods of time is safe, considering the track records of use of many of these herbs in the past versus the fact that negative effects can accumulate over time. The jury is still out but the best advice is to avoid them, as the science is pretty clear. Fortunately, some companies, such as Herb Pharm, now make pyrrolizidine-free comfrey. This can be used safely and confidently for longer periods of time.) The herb extracts (which contain PAs) are run through an ion exchange bed that removes the PAs. The finished extract contains less than 1ppm of PAs.

The herb germander (Teucrium chamaedrys) contains furano-diterpenoids, chemicals that have been shown to cause hepatitis, hepatocyte glutathione depletion, and apoptosis. In other words, it can severely damage your liver. This herb is not sold to the public, of course, but has been known in the past to be substituted for the commonly used herb scullcap (Scutellaria laterifolia). They look almost identical in the field.

Aristolochic acid is a chemical found primarily in plants from the genus Aristolochia. This chemical has been shown to cause rapid kidney failure. The Chinese herb Atristolochia fangqi has, in the past, commonly been substituted for stephania root (Stephania tetranda) and magnolia bark (Magnolia officinalis) (McGuffin et al., 1997). There have been cases of serious poisoning in Europe resulting in death, and a ban of this herb was instituted in the European Union in 1999 and later in the United States. More info.

The chemical ephedrine, found in the Chinese Herb Ma Huang (Ephedra species) has recently been pulled from the market because of the dangers it poses to the heart. This is a compex issue, covered in more detail here.

Yohimbe (Corynanthe yohimbe) is an African herb that has been used as an aphrodisiac and a weight-loss aid. Overdose can lead to numerous side effects, including paralysis. I would avoid this herb, especially as it is available as a prescription item, and there are other herbs that perform better for the same intended uses.