Herbal supplements are natural, so they must be safe, right? No, that's not true all the time.

Herbal supplements can strongly affect the body. Some don't work well with prescription medicines. This is called a medicine interaction. Herbal supplements can interact with medicines used to treat heart and blood vessel problems, such as high blood pressure and heart failure. Some of these medicine interactions can be risky.

About one-half of adults in the United States say they have used one or more supplements in the past 30 days. Almost 70% of older adults use them. But only about 25% of people who take herbal supplements tell their health care providers. And as many as 25% of people also take medicines ordered for them by their health care providers, also called prescription medicines.

Yet many herbal supplements may interact with heart disease medicines. For instance, many herbal supplements that are used often interact with the blood thinner warfarin (Jantoven).

That's why you need to talk with your health care provider before you take herbal supplements if you take prescription medicines. Your health care provider and pharmacist can help you stay away from unsafe interactions.

Many common herbal supplements interact with common heart medicines. This list covers only some interactions. Be sure to talk to your health care provider before you take any herbal supplements if you take prescription medicines.

Coenzyme Q-10

If you take coenzyme Q-10, it can lower:

• How well warfarin works
• Your blood pressure, if you also take a drug to treat high blood pressure

Danshen

Danshen can interact strongly with some heart medicines, such as:

• Blood thinners. Danshen may raise your risk of bleeding. This can happen if you also take warfarin or other blood thinners, such as clopidogrel (Plavix) or aspirin, with danshen.
• Blood pressure medicine. Danshen may make your blood pressure too low if you take danshen with a drug used to lower blood pressure. An example of a blood pressure drug is the calcium channel blocker diltiazem (Cardizem).
• Digoxin (Lanoxin). If you take danshen, it may add to the effects of digoxin. Digoxin is used to treat many heart conditions. It also might raise the risk of irregular heartbeat, also called arrhythmia.

Evening primrose

Evening primrose may raise your risk of bleeding if you also take a blood thinner, such as:

• Aspirin
• Clopidogrel
• Warfarin

Garlic

Garlic may raise your risk of bleeding if you also take a blood thinner, such as:

• Aspirin
• Clopidogrel
• Warfarin

Ginkgo biloba

Ginkgo biloba may raise your risk of bleeding if you also take a blood thinner, such as:

• Aspirin
• Clopidogrel
• Warfarin

Ginseng

If you take ginseng with warfarin, it may lessen how well warfarin works.

Hawthorn

Hawthorn might interact with:

• Beta blockers, such as atenolol (Tenormin), nadolol (Corgard) or propranolol (Inderal LA, Innopran XL)
• Calcium channel blockers, such as diltiazem, nifedipine (Procardia) and verapamil (Calan SR, Verelan)
• Nitrates, such as nitroglycerin (Nitrostat, Nitro-Dur, others) and isosorbide (Isordil, Bidil)
• Digoxin

Licorice

The herb licorice may lower warfarin levels and can add to digoxin's effects.

Saw palmetto

Saw palmetto might make your risk of bleeding higher if you also take a blood thinner, such as:

• Aspirin
• Clopidogrel
• Warfarin

St. John's wort

It's not suggested to take St. John's wort if you take blood thinners. It also may keep some medicines from working as well as they should, such as:

• Calcium channel blockers
• Digoxin
• Warfarin
• Statins, such as atorvastatin (Lipitor), lovastatin (Altoprev) and rosuvastatin (Crestor)
• Anti-rejection medicine, also called immunosuppressant medicine, such as cyclosporine (Gengraf, Neoral, Sandimmune)

If your health care provider tells you it's OK to use an herbal supplement along with medicine, be careful. Follow directions about how much medicine to take. Watch for any symptoms that you may be having a drug interaction, such as:

• Fast heartbeat
• Blood pressure changes