As many as 70% of Canadians use or have used a dietary supplement. In most cases, consumers use dietary supplements in addition to, not in place of, conventional medical treatments. This often means combining one or more supplements with conventional drugs. Many consumers assume the supplements they take are completely safe because they are "natural." As a result, many do not ask their health provider about any potential interactions with other medications or other adverse consequences.

Conventional healthcare professionals are often concerned about potential drug-supplement interactions, but how often do they really occur? And are they really significant?

The potential for interactions is huge.

The elderly population (65+) is one of the fastest growing segments of our population. They are also the largest consumers of healthcare and take the largest number of prescription drugs. About 30% of this group also takes at least one dietary supplement.


Combing a large number of drugs plus supplements makes the potential risk of an interaction increase exponentially. So far, there are no reliable estimates showing how often these interactions truly occur, or how significant they usually are. Fortunately, research in this area is growing rapidly. Interestingly, the number of scientific publications on this subject has increased over 140 times from the 1980s until 2007. Nonetheless, we are still a long way from understanding the large-scale impact drug-supplement interactions have on patient health.

Here is a list of some potentially harmful combinations but remember to always consult with a physician to determine what is best for your health needs.

Cytochrome P450 3A4 substrate

Ask your doctor if you are taking this type of drug, and if so avoid any and all of the following:

  • Grapefruit: It can affect Heart Medications, Cholesterol Medications, and often pain medications etc.
  • St Johns Wort and 5-HTP: Both can some or all of the following:

Antidepressants of the SSRI category

Oral contraceptives: St. John's wort reduces ethinyl estradiol levels by up to 15%, which can result in breakthrough bleeding, irregular menstrual bleeding, and unplanned pregnancy. Women taking oral contraceptives who also take St. John's wort should be advised to use a backup form of contraception.

Cyclosporine (Neoral, Sandimmune): St. John's wort can decrease cyclosporine levels by up to 70%, resulting in organ transplant rejection.

Imatinib (Gleevac): St. John's wort can decrease imatinib levels by 30%.

HIV protease inhibitors: St. John's wort has been shown to reduce levels of the protease inhibitor indinavir (Crixivan) by almost 60%.

  • Garlic: Similar effects as St. Johns Wort.
  • Pomegranate juice: similar effects to Grapefruit
  • Licorice (glycyrrhiza glabra): It can interact with blood pressure medication. Unless licorice is "deglycyrrhizeinated" do not take it or Ephedra (Ma Huang) if you have high blood pressure and or if you are taking blood pressure lowering medications


It can interact with Anticonvulsants and Seizure threshold lowering drugs

There certain reports linking ginkgo to seizure in people without a history of seizure and in people with well-controlled epilepsy. Ginkgo is thought to potentially lower the seizure threshold by an unclear mechanism. Ginkgo seeds contain a substance called "ginkgotoxin."

But most ginkgo supplements contain a ginkgo leaf extract which typically only contains trace amounts of the toxin. However, there is some speculation that some products may inadvertently contain higher amounts of the toxin or that some other mechanism is responsible.

Until more is known, advise patients with seizure disorder and patients taking seizure threshold lowering drugs to avoid ginkgo supplements. Some drugs that lower the seizure threshold include anesthetics (propofol, others), antiarrhythmics (mexiletine), antibiotics (amphotericin, penicillin, cephalosporins, imipenem), antidepressants (bupropion, others), antihistamines (cyproheptadine, others), immunosuppressants (cyclosporine), narcotics (fentanyl, others), stimulants (methylphenidate), theophylline, and others.

Ginger, Garlic, and Panax Ginseng and Ginkgo

These all interfere with antiplatelet drugs and Warfarin (Coumadin) and other blood thinners.

Ginkgo, for example, has been linked to several reports of spontaneous bleeding. It has also been linked to a fatal cerebral hemorrhage in a patient who took ginkgo along with ibuprofen. There is concern that combining gingko with antiplatelet

drugs such as aspirin, clopidogrel (Plavix), NSAIDs, etc, or with the anticoagulant warfarin (Coumadin) can increase the risk of bleeding. However, some preliminary research suggests that some ginkgo preparations do not substantially alter bleeding time in patients who are stable on warfarin. Until more is known, people are advised not to combine ginkgo with antiplatelet or anticoagulant drugs. Many other dietary supplements have some antiplatelet activity and might increase the risk of bleeding when combined with antiplatelet or anticoagulant drugs.

Vitamin A

This will react with Acutane and can lead to vitamin A toxicity!

Bitter orange

It can react with "QT-interval prolonging" drugs.

Bitter orange contains the stimulant synephrine. Bitter orange has largely replaced ephedra as the ingredient of choice in weight loss supplements. In one case, a combination of bitter orange with other stimulants such as caffeine prolonged the QT interval on electrocardiogram. There is concern that combining bitter orange with other drugs that prolong the QT interval could increase the risk of life-threatening ventricular arrhythmias.

Some drugs that prolong the QT interval include amiodarone (Cordarone), disopyramide (Norpace), dofetilide (Tikosyn), ibutilide (Corvert), procainamide (Pronestyl), quinidine, sotalol (Betapace), thioridazine (Mellaril), and many others.


It can affect Levothyroxine (Synthroid, and others)

Most of us remember that calcium can bind antibiotics like the quinolones and tetracycline, and also bisphosphonates. But not as many people realize that calcium can also bind and reduce absorption of levothyroxine. To avoid this interaction, people should take levothyroxine and calcium supplements at least four hours apart.

Noni juice or Supplemental Potassium. They can affect ACE inhibitors

Noni juice contains significant amounts of potassium

This isn't a problem for most people, but could result in hyperkalemia (potassium excess) in people with renal dysfunction or in people taking other drugs that increase potassium levels such as ACE inhibitors. Both should be avoided if taking an "ACE" inhibitor type of blood pressure medication.


It can interfere with "hepatotoxic drugs".

Kava has been linked to numerous reports of hepatotoxicity. There is concern that

combining kava with drugs that are potentially hepatotoxic might increase the risk of liver damage. Some potentially hepatotoxic drugs include acarbose (Precose, Prandase), amiodarone (Cordarone), atorvastatin (Lipitor), carbamazepine (Tegretol), fenofibrate (Tricor), fluvastatin (Lescol), gemfibrozil (Lopid), isoniazid, itraconazole, (Sporanox), ketoconazole (Nizoral), leflunomide (Arava), lovastatin (Mevacor), methotrexate (Rheumatrex), nevirapine (Viramune), niacin, nitrofurantoin (Macrodantin), pioglitazone (Actos), pravastatin (Pravachol), ritonavir (Norvir), rosiglitazone (Avandia), simvastatin (Zocor), tamoxifen, terbinafine (Lamisil), valproic acid, zileuton (Zyflo), and others.


Interacts with Benzodiazepine.

Taking valerian together with a benzodiazepine such as: Alprozolam (Xanax), Chlordiazepoxide (Libriu), Clonazepam (Klonopin), Diazepam (Valium), Flurazepam (Dalmane), Lorazepam (Ativan), Temazepam (Restoril), and Triasolam (Halcion) can cause an accumulative sedative effect.


  • Natural Medicines Comprehensive Database online clinicians database
  • IBIS Interactions CD Rom compilation
  • Reuters Medical Database
  • Prescription for Natural Cures. Dr. J. Balch