Avoiding interactions when using herbal supplements

Herbal supplements are often used to enhance a person’s health and to help with symptoms or diseases - but just because they’re natural doesn’t mean they’re safe. It’s important to always be cautious since herbal supplements, and some vitamins, have the potential to interact with other medications and may be contradicted in certain medical conditions.

Here are a few of the most common herbal supplements, and some important precautions to keep in mind:

Calcium may decrease the effectiveness of certain antibiotics, some osteoporosis medications, and thyroid medication. Reduce this interaction by taking calcium several hours (at least four) apart from the other medications.

Vitamin E may enhance the anticoagulant (anti-clotting) effects of blood thinners, and increase the risk of bruising and bleeding. Patients with a history of stroke should avoid Vitamin E, since a study has shown it’s associated with an increased risk of mortality. 

Iron absorption can be reduced if taken with foods that contain calcium. Patients with decreased levels of iron should take calcium supplements and calcium-containing antacids several hours before or after any iron preparations. Patients taking iron salts and levothyroxine, a thyroid medication, should also separate these by at least four hours to avoid decreased effectiveness. Iron preparations may also decrease the effectiveness of certain antibiotics, like ciprofloxacin and tetracycline, methyldopa (a blood pressure medication), and levodopa (an anti-parkinson medication) and so they should also be separated by at least two hours.

Coenzyme Q10 may decrease the effects of the anticoagulant warfarin (a medication that stops blood from clotting) and lower INR (international normalized ratio, a blood test used to determine the effects of warfarin). Close monitoring of coagulation status is needed. Patients taking other medications for high blood pressure should also use caution as it may also lower blood pressure.

Garlic (raw or extract) can increase the risk of bleeding when taken with other drugs (e.g. warfarin, clopidogrel, aspirin) or herbs with similar properties, like ginseng , green tea and red clover. Monitor for signs and symptoms of bruising and bleeding. Patients scheduled for surgery or other invasive procedures (e.g., dental work) should discontinue these herbs two weeks prior to the procedure. If combined with medications that lower blood pressure, garlic may have additive effects and should be used with caution. It may also decrease the effectiveness of ritonavir, an antiretroviral drug, and so this combination should be avoided.

American ginseng may affect blood glucose levels and, when taken with antidiabetic drugs like glyburide, rosiglitazone, and insulin, may cause low blood sugar, so patients with poor glucose control should avoid ginseng. Ginseng may also decrease the anticoagulant effect of warfarin and lower INR, and so this combination should be avoided. Patients should discontinue ginseng at least two weeks prior to a scheduled surgery.

Glucosamine and chondroitin was once thought to raise blood glucose level in people with diabetes. This has since been refuted.  Patients should discontinue glucosamine at least two weeks prior to scheduled surgery. Glucosamine may increase the anticoagulant effect of warfarin and raise INR. 

St. John’s Wort decreases the effectiveness of some medications and should be avoided with the following:  anticoagulants, antiretrovirals, antifungals, immunosuppressive agents, narcotics, digoxin (a heart medication), and hormonal contraceptives. Using St. John’s Wort with medications that affect the level of serotonin in the brain (such as some antidepressants and migraine medications) may increase the risk of serotonin syndrome, a potentially life-threatening condition, and this combination should therefore be avoided. 

Green tea and caffeine supplements contain catechins that can theoretically increase the risk of bleeding when used with antiplatelet or anticoagulant drugs. Patients on nadolol, a blood pressure medication, should minimize green tea consumption.  Patients on lithium who increase/decrease caffeine consumption should also have their lithium blood levels monitored. Ciprofloxacin, an antibiotic, may prolong the presence and the effects of caffeine in the body.

This is not a comprehensive list of all drug-herbal supplement interactions. Please always consult your pharmacist before taking a natural health product or supplement.

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