When used properly, many herbal supplements may be safe and possibly beneficial to health. However, a few natural supplements can cause life-threatening problems or dangerous interactions with medications.

Natural doesn’t always mean safe when it comes to herbal supplements, according to the Mayo Clinic Health Newsletter. The newsletter covers some of the known interactions between herbal supplements and medications:

Garlic, ginseng, ginger and feverfew:
Patients who take anti-clotting medications such as aspirin, warfarin (Coumadin) and clopidogrel (Plavix) should avoid these natural supplements. They may increase the risk of bleeding. Supplements chondroitin and glucosamine also may interfere with warfarin.

Ginkgo:
Ginkgo may increase the risk of bleeding in patients taking anti-clotting medications. Ginkgo can counteract the blood pressure-lowering benefits of thiazide diuretic drugs. It also can interfere with anti-seizure medications.

Kava:
Kava is a sedative herb and is associated with serious liver problems, even when taken for a short time. Many medications, such as cholesterol-lowering drugs, pose a risk of liver damage. Taking kava supplements may increase the risk of liver problems even more.

St. John’s wort:
This supplement can greatly increase or decrease the potency of many medications and cause serious side effects. Patients who take antidepressants, anti-blood-clotting drugs, certain asthma drugs, immune-suppressing medications or steroids should probably avoid St. John’s wort.

S-adenosylmethionine (SAM-e):
This can cause serious side effects when taken with antidepressant medications that affect serotonin.

It’s always best to keep health care providers informed about natural herbal supplement you use, especially when starting a new medication or preparing for a medical procedure. Some herbal supplements need to be discontinued two to three weeks before certain surgical procedures, because they affect blood clotting, response to sedation and blood pressure control.