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Speed kills, especially when it comes to pills. Everyone is in such a hurry these days that it’s rare for physicians to provide detailed instructions about how to take prescribed medicine.

Pharmacists are overwhelmed, so they hardly ever interact directly with patients to give them advice. Pharmacy technicians may be good at counting pills and ringing up bills, but they don’t have the training to counsel people about food and drug interactions.

Patients also are pressed for time. Few people take the time to read instructions that might be provided with a prescription or over-the-counter medicine. But how you swallow your medicine matters.

Do you take your pills at breakfast? If you wash them down with orange or apple juice, drink a cup of tea or coffee or eat yogurt or bran cereal, you could be reducing the effectiveness of certain medications.

People taking alendronate (Fosamax) for osteoporosis, for example, have been drilled that the pills must be taken on an empty stomach at least half an hour before the first cup of coffee or tea (with tap water, not fancy mineral water). Otherwise, you might as well throw the pill away, as it will not be absorbed adequately.

Taking the blood pressure pill aliskiren (Tekturna) with apple juice dramatically decreases the amount of medicine that gets into the bloodstream. Coffee or tea can reduce the absorption of the thyroid hormone levothyroxine (Levoxyl, Synthroid, etc.). So can mineral supplements like calcium or iron, found in many multivitamins.

When doctors prescribe warfarin (Coumadin) for a blood clot in the leg or the lung, they may warn their patients to go easy on green vegetables. Broccoli, cabbage, salad and spinach all are rich in vitamin K, which could counteract the anticoagulant activity of warfarin.

Far more controversial, however, is the cranberry-Coumadin interaction. One study found no interaction between warfarin and cranberry juice (British Journal of Clinical Pharmacology, July 2010).

There are, however, numerous case reports in the medical literature describing an increased bleeding risk when people on warfarin also consume cranberry sauce or juice. One patient had a dramatic rise in the blood-thinning effect (INR) after starting to drink cranberry juice. He died six weeks later of a hemorrhage (BMJ, Dec. 20, 2003).

One reader recently shared this experience: “My husband’s INR increased one year around Thanksgiving, when we had cranberry sauce several days in a row. He also reacted one spring after we had rhubarb sauce several days running.”

Dozens of drugs interact with grapefruit, but warnings are not always prominent. Some of the most popular include cholesterol-lowering meds such as atorvastatin, lovastatin and simvastatin.

The powerful heart drugs amiodarone and dronedarone (Multaq) become more dangerous with grapefruit on board.

Since foods and beverages can have a profound impact on many of the medicines you take, it is worth spending a few minutes to quiz your doctor and pharmacist about potential interactions. Don’t be in such a hurry that you put your health at risk.