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• Vitamin K can antagonize the anticoagulant effect of warfarin.
• Vitamin B₆ increases the metabolism of levodopa, producing decreased anti-Parkinson's effects.
• Calcium, magnesium and aluminum found in food supplements or antacids bind with the antibiotic TCN, resulting in decreased absorption and antibiotic effect of the drug.
• Calcium in some nutritional supplements can reduce the bioavailability of some fluoroquinolone antibiotics, like ciprofloxacin, enoxacin and phenytoin, resulting in decreased antibiotic activity and loss of seizure control.

Drug-disease interactions: Certain drugs can worsen already acute or chronic conditions. For example, the medication prednisone can aggravate congestive heart failure and cause fluid overload. Another reason drug-disease interactions are particularly dangerous is that manifestations of adverse reactions may be very subtle, requiring long-term monitoring.

Drug-herbal interactions: Every year, U.S. adults spend billions on all kinds of natural products and herbal supplements. It's a booming industry indeed, and many natural products bring significant benefit to health-conscious consumers. Still, many Americans underestimate the potency of herbal products because they don't come with a prescription and because adverse side effects from these products, when taken alone, are rare. But throwing pharmaceuticals in with natural blends can create big problems.

Research shows that an estimated 70 percent of patients may not be disclosing to their physicians which herbal supplements they're taking. Your physician should be asking about your use of herbal or natural products and other OTC medications in order to evaluate the potential for adverse interactions. And even if they aren't asking, it is your job to provide that information to them.

The Best Way to Protect Yourself: Be Proactive

Your physician should do more than prescribe medication; he or she should inform you in full about the risks of taking any medication. But it's your health on the line, not your doctor's. Take responsibility for your own health by asking questions - however minor they may seem - and explaining your health history (including other medications you may be taking) and health goals to your physician. Be inquisitive:

• Are there any lifestyle changes (e.g., diet, exercise) I can make in order to avoid taking a particular medication?
• How long has this prescription medication been on the market? In what manner and for how many months did the drug undergo testing and trials?
• Are there similar drugs that have been on the market longer (and thus have proven over time to be effective and with limited risk of side effects)?
• Where can I find a full list of the drug's potential side effects?
• Will a new prescription cause an adverse reaction with any herbs, vitamins, OTC medications, or prescription drugs I am already taking? What is the risk of such a reaction?
• Will I need to change my current diet or cut out any particular foods while taking this medication?