While herbs and vitamins are much safer than pharmaceutical drugs, there are some potential adverse reactions when taking them in combination.

The A-Z Guide to Drug-Herb-Vitamin Interactions offers a comprehensive list by medications, here we will focus more on popular herbs, foods and vitamins, and how they react with selected drugs.

Understanding Why Drugs and Herbs Interact

There are two fundamental mechanisms that contribute to interactions: pharmacokinetic and pharmacodynamic:

Pharmacokinetic interactions refer to changes that occur as medicines move in and out of the body, such as with absorption, distribution, metabolism and elimination.

Pharmacodynamic interactions refer to how medicines actually behave inside the human body, as they can sometimes increase or cancel out the effectiveness of another.

Absorption, distribution, metabolism and elimination are four cycles that all medicines go through in the body. After a medicine is taken, it is absorbed from the intestines, distributed throughout the body, metabolized (broken down) in the liver, and finally, eliminated from the body through the kidneys.

Many factors may interrupt these cycles, leading to interactions. For example, ingestion of an antacid or anti-ulcer medication will reduce the acidity of the stomach, therefore decreasing the absorption of other medicines and herbs. In addition, some drugs may interfere with blood circulation and affect the distribution of medicines or herbs to the affected parts of the body. Finally, some drugs may be harmful to the liver or kidneys, impairing the ability of the body to break down and eliminate the medicines or herbs.

The extent and severity of each interaction will vary depending on specific circumstances such as dosage, sensitivity. metabolic rate and the type of drugs and herbs taken.

Common Herb-Drug Interactions

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Aloe Vera: Should not be taken with Digoxin (heart medication). The combination may contribute to dangerously low potassium levels.

Ephedra: For many years ephedra was the main ingredient in just about every weight loss product on th emarket. Ephedra was said to increase heart rate, cardiac output and raise blood pressure.

Because ephedra is a potent herb and is prone to misuse, it has been reported to cause more adverse reactions and caused more deaths than any other herb sold in the United States. Although t has been used for thousands of years in China to treat various respiratory conditions, it is no longer available in most countries.

Hawthorn: Effective in reducing angina attacks by lowering blood pressure and cholesterol levels, it should not be taken with Lanoxin (Digoxin), a medication prescribed for heart ailments. The mix can lower the heart rate too much.

Ginger: A gram or so of powdered ginger can help ease nausea, but it can also interfere with platelet action. This means that ginger shouldn't be taken with Aspirin, Warfarin or other blood thinners.

Garlic: Garlic combined with diabetes medication can cause a dangerous decrease in blood sugars. Often used to help rein in blood pressure and high cholesterol, as well as being an effective natural antibiotic, garlic or garlic pills taken in large doses can also thin the blood. Not surprisingly, people taking warfarin, regular doses of aspirin, or other blood thinners should not use garlic for anything other than seasoning.

Ginko Biloba: Used to improve blood circulation and in the treatment of memory loss, Ginko has blood-thinning properties and should not be used with anticoagulants or before surgery.

Goldenseal: Goldenseal is used for coughs, stomach upsets, menstrual problems, as a natural antibiotic and even arthritis. However, the plant's active ingredient will raise blood pressure, complicating treatment fo rthose taking antihypertensive medications, especially beta-blockers. For patients taking medication to control diabetes or kidney disease, this herb can cause dangerous electrolyte imbalance.

Feverfew: Feverfew is a natural remedy for migraine headaches that should never be taken with Imitrex or other migraine medications. It can result in the patient's heart rate and blood pressure rising.

Guarana: Guarana is an alternative remedy being used as a stimulant and diet aid that contains 3-5 percent more caffeine than a cup of coffee. Those taking medications that advise against caffeine consumption should avoid taking this stimulant.

Kava: Kava is an herb used for the treatment of anxiety, pain and muscle aches that should not be taken with substances that affect the central nervous system such as alcohol, barbituates, anti-depressans and antipsychotic drugs.

Licorice: Licorice may offset the actions of immunosuppressive drugs, including corticosteroids (prescribed for a wide range of disorders from asthma to cancer). Licorice may also reverse the effects of blood pressure medications and worsen the adverse side effects of the heart medication Digoxin. it may also increase the side effects produced by oral contraceptives.

Milk Thistle: Used to support liver functions, this herb should not be taken with immunsuppressive drugs and can be dangerous for transplant patients because it can interact with transplant drugs such as Cyclosporine. (Milk Thistle does protect the liver from drug damage and helps reduce drug toxicity in many instances.)

St. John's Wort: A popular herb for the treatment of mild depression, St. John's Wort may mildly mimic MAOI drugs and should not be used when taking antidepressant medications such as phenelzine. St. John's Wort can also duplicate the effects of SSRIs such as Prozac and Zoloft and should not be taken together.

Valerian: A proven sleep aid, valerian may trigger extreme drowsiness if mixed with barbituates. It is also unwise to mix this herb with alcohol.

White Willow: White Willow is an herb traditionally used for fever, headache, pain and rheumatic complaints that may exhibit similar reactions as aspirin (which is derived from White Willow).

Yohimbe: This herb is most often used for impotence and to increase sexual desire. It should not be used with antidepressants or psychotropic drugs. The combination may increase the risk of hypertension.

Common Vitamin-Drug Interactions

  • Vitamin C: The absorption of Vitamin C is reduced by Aspirin.
  • Vitamin D: Phenytoin can reduce serum Vitamin D levels.
  • Vitamin K: May reduce the effects of anticoagulants such as Nnicoumaline/Acenocoumarol, Phenindione, and Warfarin.
  • Calcium: Combined with diuretics may contribute to a higher risk of hypercacaemia.
  • Folic Acid: Can contribute to reduced serum levels of anticonvulsant drugs.
  • Iodine: Combined with diuretics can lead to an increased risk of hypothyroidism.
  • Iron: Can lead to reduced absorption of the following drugs: dopaminergics (Levodopa), penicillamine, quinolone antibiotics (Ciprofloxacin, Norfloxacin, Ofloxacine).
  • Potassium: Combined with ACE-inhibitors, Cyclosporin and potassium sparing diuretics, can lead to hyperkalemia.
  • Zinc: Combines with iron and Tetracycline antibiotics reduces absorption of zinc (and vice versa).

Common Food-Drug Interactions

  • Black Licorice: People taking digoxin should avoid eating licorice. This combination may produce irregular heart rhythms and cardiac arrest. Licorice and diuretics can produce dangerously low potassium levels, putting a patient at risk for numbing weakness, muscle pain and even paralysis. Licorice can also interact with blood pressure medication or any calcium channel blockers.
  • Bananas: Due to their high potassium content, bananas do not combine with heart drugs well and can lead to dangerous potassium build-up.
  • Cheese and Sausage: These two foods, as well as other foods high in tyramine, combined with MAO inhibitors can cause a potentially fatal rise in blood pressure.
  • Grapefruit Juice: Grapefruit juice interacts with calcium channel blockers (including calan, procardia, nifedipine, and verapamil), cholesterol control medications, some psychiatric medications, estrogen, oral contraceptives, and many allergy medications (seldane, hismanal). The juice modifies the body's way of metabolizing the medication, affecting the liver's ability to work the drug through a person's system.
  • Orange Juice: OJ shouldn't be consumed with antacids containing aluminum. The juice increases the absorption of the aluminum. Orange juice and milk should also be avoided when taking antibiotics. The juice's acidity decreases the effectiveness of antibiotics, as does milk.
  • Milk: Milk doesn't mix well with laxatives containing bisacodyl (Corectol and Dulcolax). And, as mentioned above, shouldn't be taken with antibiotics as it decreases antibiotic effectiveness.
  • Leafy Green Vegetables: High in Vitamin K, leafy greens should not be eaten in large quantities while taking Coumadin. These vegetables may negate the affects of the drug and cause blood clotting.
  • Caffeinated Beverages: Caffeine and asthma drugs taken together can cause excessive excitability. Caffeine is also contraindicated while taking homeopathic medicines.
  • Grilled Meat: Grilled meat can lead to problems for those on asthma medications containing theophyllines. The chemical compounds formed when meat is grilled may prevent this type of medication from working effectively, increasing the possibility of an unmanageable asthma attack.
  • High-Fat Diets: Consuming a high-fat diet while taking anti-inflammatory and arthritis medication can cause kidney damage and leave the patient feeling drowsy and sedated.
  • Alcoholic Drinks: Alcohol can increase the depressive effects of medications such as benzodiazepines, antihistamines, antipsychotics, antidepressants, muscle relaxants, narcotics or any sedative drug.
  • Strawberries, Raspberries, Spinach and Rhubarb: These each contain oxalic acid which can aggravate kidney and bladder stones in susceptible individuals, and reduce the body's ability to absorb iron and calcium.
  • Raspberries: Raspberries contain a natural salicylate that can cause an allergic reaction in aspirin-sensitive people.
  • Horseradish: A very high dose of horseradish can cause vomiting or excessive sweating. Those suffering from hypothyroidism should avoid it.
  • Turmeric: This herb/spice should be avoided by persons with symptoms from gallstones.

Historically, herbs and drugs have been two very different treatment modalities which have rarely, if ever, been used together. The line that separates herbs and drugs, however, has been blurred in recent decades with the increased accessibility to the general public of different forms of treatment.

It is not uncommon for a person to seek the services of several physicians or natural health practitioners for the same ailment. As a result, that person may be taking multiple drugs, herbs and vitamins simultaneously – which, as has now been shown, can result in serious and unhealthy interactions.

Safe, Effective Herbal and Homeopathic Remedies

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With over 500,000 customers worldwide and more than 250 herbal remedies and homeopathic remedies, we’re confident that you’ll find the holistic health products you need.

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References and Recommended Reading:

Principles of Medical Pharmacology by H. Kalant, W. Roschlau
A-Z Guide of Drug-Herb-Vitamin Interactions by Healthnotes
The Patient's Guide of Natural Healing by Jonathan Wright, M.D.
Holistic Herbal by David Hoffman
The Encyclopedia of Nutrition and Good Health by Robert A. Ronzio, Ph.D.
The Herb Bible by Earl Mindell
The Complete Medicinal Herbal by Penelope Ody
School of Natural Healing by Dr. John R. Christopher
The New Age Herbalist by Richard Mabey


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