You may think herbal supplements are safe because they're labeled "natural." But many herbal supplements contain active ingredients that can harm you if taken with certain prescription or over-the-counter (OTC) drugs.

In addition, some medical situations increase your risk of adverse effects if you take herbal products. Talk to your doctor before taking any herbal products if you're pregnant or breast-feeding or if you have:

• High blood pressure
• Thyroid problems
• Depression or other psychiatric problems
• Parkinson's disease
• Enlarged prostate gland
• Blood-clotting problems
• Diabetes
• Heart disease
• Epilepsy
• Glaucoma
• History of stroke or organ transplant

It's a good idea to talk to your doctor about any herbal supplements you take, no matter what type of medication you're using or the condition for which you're being treated.

Here are 14 herbs and the prescription and OTC drugs you shouldn't take with them:

Capsicum
Avoid taking with:

• Angiotensin-converting enzyme (ACE) inhibitors — used for diabetic kidney disease, heart failure, high blood pressure

• Theophylline (Elixophyllin, Uniphyl) — an asthma medication

• Sedatives
• Antidepressants

Capsicum may increase the absorption and the effect of these drugs. It may also increase the likelihood of developing a cough if used with ACE inhibitors.

Coenzyme Q-10
Avoid taking with:

• Warfarin (Coumadin) — a blood-thinning medication
• Chemotherapy

The use of warfarin and coenzyme Q-10 together increases your risk of excessive bleeding. Coenzyme Q-10 may reduce the effectiveness of some chemotherapy. Some drugs, such as those used to lower cholesterol (lovastatin, pravastatin, simvastatin), blood sugar (glyburide, tolazamide) and blood pressure (beta blockers such as Inderal, Lopressor), can alter coenzyme Q-10's effectiveness. Also, people with diabetes should be aware that coenzyme Q-10 may decrease their need for insulin.

Dong quai
Avoid taking with:

• Warfarin (Coumadin) — a blood-thinning medication
• St. John's wort
• Antibiotics (sulfonamides, quinolones)

The combination of dong quai and warfarin may increase your risk of bleeding. Using St. John's wort or certain antibiotics with dong quai may increase your skin's sensitivity to the sun.

Echinacea
Avoid taking with:

• Anabolic steroids
• Amiodarone (Cordarone, Pacerone) — used to treat an irregular heartbeat (arrhythmia)
• Methotrexate (Rheumatrex) — used to treat rheumatoid arthritis
• Ketoconazole (Nizoral) — an antifungal medication
• Cyclosporine (Neoral, Sandimmune) — an immunosuppressant
• HIV protease inhibitors — human immunodeficiency virus (HIV) medications
• Benzodiazepines (Alprazolam, Valium) — anti-anxiety medications
• Calcium channel blockers — used to treat high blood pressure and heart disease

Echinacea shouldn't be combined with other drugs that can cause liver damage. And because this herb may stimulate the immune system, it may interfere with the effects of immunosuppressants.

Echinacea may also elevate the levels of HIV protease inhibitors, calcium channel blockers and anti-anxiety drugs in the blood, increasing your risk of side effects.

Ephedra
In late December 2003, the Food and Drug Administration announced the ban of ephedra from the marketplace because of health concerns. Ephedra increases your risk of heart attack, stroke, seizures and death. Combined with caffeine, decongestants, stimulants and other drugs, it becomes especially risky.

Ephedra is a potent herb that's present in many products, especially those designed to give you pep or help you lose weight. It goes by many names, such as ma-huang, herbal ecstasy, mahuang, mahuanggen and ma huang root. Any "natural" product that claims to cause weight loss or increase energy may have ephedra in it. Carefully review the product's contents with your doctor or pharmacist before assuming it doesn't.

Feverfew
Avoid taking with:

• Aspirin
• Ticlopidine (Ticlid) — blood-thinning medication
• Clopidogrel (Plavix) — blood-thinning medication
• Dipyridamole (Persantine) — blood-thinning medication
• Warfarin (Coumadin) — blood-thinning medication

These medications can reduce blood clot formation. Feverfew may increase this effect, causing spontaneous and excessive bleeding.

Garlic
Avoid taking with:

• Aspirin
• Ticlopidine (Ticlid) — blood-thinning medication
• Clopidogrel (Plavix) — blood-thinning medication
• Dipyridamole (Persantine) — blood-thinning medication
• Warfarin (Coumadin) — blood-thinning medication
• Cyclosporine (Neoral, Sandimmune) — an immunosuppressant
• Saquinavir (Fortovase, Invirase) — an HIV protease inhibitor

Combined with garlic, anticoagulant medications may cause spontaneous and excessive bleeding. Garlic may decrease the effectiveness of immunosuppressants and HIV protease inhibitors.

Garlic may cause lower levels of blood sugar, which may decrease your need for insulin if you have diabetes. If you take insulin and garlic together, monitor your blood sugar carefully and report any changes to your doctor.

Ginger
Avoid taking with:

• Aspirin
• Ticlopidine (Ticlid) — blood-thinning medication
• Clopidogrel (Plavix) — blood-thinning medication
• Dipyridamole (Persantine) — blood-thinning medication
• Warfarin (Coumadin) — blood-thinning medication
• H2 blockers and proton pump inhibitors — acid-blocking medication

Ginger may increase the effect of anticoagulants, which may cause excessive bleeding. It may also increase the production of stomach acid, which could counteract the effects of antacid medications.

Ginger may lower your blood pressure or blood sugar levels, which may reduce your need for blood-pressure-lowering medications or insulin if you have diabetes. Monitor your blood pressure or blood sugar levels if you take these medications and report any changes to your doctor.

Ginkgo
Avoid taking with:

• Aspirin
• Ticlopidine (Ticlid) — blood-thinning medication
• Clopidogrel (Plavix) — blood-thinning medication
• Dipyridamole (Persantine) — blood-thinning medication
• Warfarin (Coumadin) — blood-thinning medication
• Antidepressants
• Antipsychotic medications
• Insulin

Ginkgo may increase the anticoagulant effect of these drugs and has the potential to cause spontaneous and excessive bleeding when used in conjunction with these medications. It can also increase the amount of antidepressant medication in your blood. When combined with antipsychotic medications, ginkgo may cause seizures. Ginkgo also affects insulin levels, so if you're taking the two together, monitor your glucose levels carefully.

Ginseng
Avoid taking with:

• Warfarin (Coumadin) — blood-thinning medication
• Phenelzine (Nardil) — an antidepressant
• Digoxin (Lanoxicaps, Lanoxin) — heart medication
• Insulin and oral antidiabetic medications

Used with warfarin, ginseng can increase your risk of bleeding problems. Ginseng with phenelzine may cause headache, trembling and manic behavior. Ginseng may interfere with digoxin's pharmacologic action or the ability to monitor digoxin's activity.

Ginseng can reduce blood sugar levels in people with type 2 diabetes (formerly called adult-onset or noninsulin-dependent diabetes). Without careful glucose monitoring, the use of ginseng with insulin or oral antidiabetic medications may cause dangerously low blood sugar levels.

Ipriflavone
Avoid taking with:

• Warfarin (Coumadin) — blood-thinning medication
• Antipsychotics
• Tacrine (Cognex) — an Alzheimer's disease medication
• Theophylline (Elixophyllin, Uniphyl) and zafirlukast (Accolate) — asthma medications
• Caffeine
• Tamoxifen (Nolvadex) — a cancer treatment and prevention medication
• Cyclobenzaprine (Flexeril) — a muscle relaxant
• Celecoxib (Celebrex) — pain-relieving arthritis medication
• Nonsteroidal anti-inflammatory medications — pain-relieving medication

Ipriflavone affects the way these drugs are metabolized, usually increasing the levels of the medications in the blood and the effects of the drugs.

Kava
Avoid taking with:

• Sedatives
• Sleeping pills
• Antipsychotics
• Alcohol
• Drugs used to treat anxiety or Parkinson's disease

Combined with these drugs, kava can produce deep sedation and, in some cases, even coma. In late 2001, following reports from Europe of liver problems in several people who used kava, the Food and Drug Administration started investigating the safety of this herb. Until more is known, don't start taking kava or products that contain kava. If you already do so, contact your doctor for advice and ask if you need liver function tests to check for unexpected liver problems. Don't take kava if you have a history of liver problems, if you're depressed, or if you take antidepressants or prescription sedatives.

Melatonin
Avoid taking with:

• Nifedipine (Adalat, Procardia) — used to lower blood pressure and treat heart disease
• Fluvoxamine (Luvox) — an antidepressant

Melatonin may reduce nifedipine's ability to lower blood pressure, which could lead to an increased heart rate and blood pressure level if these drugs are taken together. Fluvoxamine slows the metabolism of melatonin, which may result in excessive sleepiness.

St. John's wort
Avoid taking with any prescription medications. In particular, avoid taking St. John's wort and:

• Antidepressants
• HIV protease inhibitors — used to treat HIV/AIDS
• Non-nucleoside reverse transcriptase inhibitors — used to treat HIV/AIDS
• Digoxin (Lanoxicaps, Lanoxin) — heart medication
• Theophylline (Elixophyllin, Uniphyl) — an asthma medication
• Cyclosporine (Neoral, Sandimmune) — an immunosuppressant
• Chemotherapy
• Oral contraceptives
• Nifedipine (Adalat, Procardia) and diltiazem (Cardizem, Dilacor) — blood pressure and heart disease medications
• Warfarin (Coumadin) — blood-thinning medication
• Alcohol

• Tamoxifen (Nolvadex) — a cancer treatment and prevention medication

St. John's wort has been shown to affect your body's metabolism of all of these drugs. Many other drugs are likely to be affected, too. Until more is known about St. John's wort's ability to alter the metabolism of pharmaceutical medications, it's probably best not to combine such medications with St. John's wort.

Also, the combination of St. John's wort with some antidepressants, such as selective serotonin reuptake inhibitors, may cause an excess of serotonin (serotonin syndrome). Typical symptoms include headache, stomach upset and restlessness.

St. John's wort may reduce the effectiveness of some oral contraceptives. Use another form of birth control while taking St. John's wort.