Foods and Medications That Don’t Mix

(This article previously appeared on Grandparents.com.)

What's the biggest mistake many people over 50 make when it comes to their medications? Failing to read the warning labels that come with their prescriptions, according to a study done by researchers at Kansas State University.

And that's bad news. Not knowing what foods and drinks to skip while you're on Rx drugs can cause serious side effects or lower the effectiveness of your medications.

To stay safe: Get the facts from your doctor and follow up with a 10-minute chat with your pharmacist to learn the ins and outs of your prescription — and what foods and beverages to avoid while you're on it, suggests Lauren Aleksunes, an assistant professor at the Ernest Mario School of Pharmacy at Rutgers University in New Jersey. In the meantime, here's what to beware of:

Brand names include: Monopril, Zestril, and Univasc. Most generic ACE inhibitors end with the letters "pril."

About 54 percent of boomers between 55 and 64 have high blood pressure and nearly two thirds of those over 65 do, according to the Centers for Disease Control and Prevention (CDC). If you're one of them, you may be controlling your blood pressure with an ACE inhibitor.

These meds can raise the potassium levels in your body which can cause your heart to beat irregularly, leading to cardiac arrest in severe cases. To keep levels from climbing even higher, limit potassium-rich foods like bananas, spinach and other leafy greens, sweet potatoes and salt substitutes that contain potassium.

What you need to know: "A banana one day and a spinach salad the next should be okay," says Aleksunes. But if you're going to make major changes in your diet, especially by adding in more fruits and vegetables, check with your doctor first.

Also check with your practitioner or pharmacist if you're on a diuretic to lower your blood pressure; certain ones can increase your potassium levels, too.

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Brand names include: Lipitor, Mevacor, Zocor, and Lipex. Generic names: atorvastatin, lovastatin, or simvastatin

About 71 million Americans have high cholesterol, according to the CDC, and about a third of them take statins to keep it in check. If you're washing down your Lipitor (or any of the medications listed above) with a glass of grapefruit juice, stop.

Grapefruit can prevent the drug from being broken down by the liver, increasing the risk that it will accumulate in your body to toxic amounts, says Aleksunes.

What you need to know: While the Food and Drug Administration advises people on these meds not to drink more than a quart of grapefruit juice a day, Aleksunes suggests staying away from both fruit and juice altogether. But do check with your doctor or pharmacist about your particular prescription; you can mix grapefruit and other cholesterol drugs.

Brand names: Coumadin and Jantoven. Generic name: warfarin

People who have had heart attacks or at a high risk of developing blood clots are sometimes put on warfarin, a drug that thins the blood so it can circulate more easily. Vitamin K, found mostly in leafy greens, can block the effects of warfarin, putting you at risk of developing a blood clot.

That's why experts recommend limiting leafy greens to a single serving a day — and eating the same amounts every day. Garlic and ginger, which can increase warfarin's blood-thinning abilities, may be off the menu, too, along with cranberries (and cranberry juice), but check with your doctor or pharmacist to see how much is too much.

What you need to know: Greens that are particularly high in vitamin K are kale, spinach, collard, parsley, and Swiss chard. Green tea also contains this nutrient, so talk to your doctor if you drink it regularly.

Brand names include: Sumycin, Dynacin, Monodox. Generic names: tetracycline, doxycycline, minocycline

If you have a urinary tract infection or Lyme disease, your doctor may prescribe tetracycline or doxycycline to fight off the infection. After your daily dose, avoid eating dairy for a couple of hours.

Here's why: Calcium binds to the antibiotic and prevents your body from absorbing it, says Aleksunes. Instead, it stays in your intestines and ends up in the toilet bowl the next time you have a bowel movement. "At that point, you're just wasting your money," she adds.

What you need to know: The antibiotics your grandkids take for ear infections or strep don't have the same dairy restriction. So it's okay to give them a milk or yogurt chaser after they've taken a spoonful of antibiotics.

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Brand name: Plavix

To keep strokes and heart attacks at bay in high-risk patients, a doctor's first line of defense is frequently aspirin or another anti-platelet drug like Plavix. Both keep the blood from clotting.

Two foods that can affect the way anti-platelets work — and up your risk of excessive bleeding — are garlic and ginger, since they also have blood-thinning properties in high doses. Talk to your doctor about how much garlic is too much; it could be that garlic-flavored seasonings are okay.

What you need to know: If your doctor's put you on baby aspirin instead of the higher-dose kind, check to see if this restriction applies.

Brand names include: Synthroid, Levoxyl, Levothroid. Generic names: levothyroxine

Women are at greater risk for thyroid problems than men, and that risk goes up for those over 50. If your thyroid gland isn't producing enough of the hormone — you're tired all the time, your hair is falling out and you're gaining weight — you'll have to take medications to raise your levels to normal.

Eating tofu or drinking soymilk can prevent your body from absorbing the medicine, guaranteeing your symptoms continue. Walnuts and thyroid meds don't mix either—like soy, they prevent your body from absorbing levothyroxin—so sub in pecans (also high in omega 3s) in salads and snacks.

What you need to know: You may not have to give up soy products all together, but you do need to keep your doctor and pharmacist in the loop about how much soy you eat, so you can get the correct dose of medications. Also let your practitioner know when you make any major changes to your diet.

Brand name includes: Xanax, Klonopin, Valium, Ativan. Generic names: alprazolam, clonazepam, diazepam, lorazepam

There were nearly 50 million prescriptions of Xanax filled in 2011, according to The New York Times, making it one of the best-selling Rx drugs on the market. (Anti-anxiety meds like Ativan and Valium are big sellers, too.) These meds act as sedatives, binding with the brain's natural tranquilizers to calm you down. When you mix one of these drugs with alcohol, the side effects intensify — you feel drunker, sleepier, have trouble remembering things. It can also slow down the rate of your breathing.

What you need to know: Xanax is the fastest-acting anti-anxiety drug, so mixing it with alcohol is potentially more dangerous.

The average boomer takes four meds a day, while about a third of those over 65 are taking 10. When you're popping that many pills, there are bound to be scheduling conflicts and contraindications.

Some drugs are best taken on an empty stomach, others should be taken at meals. To avoid mix-ups and bad food interactions, fill all your prescriptions at the same pharmacy, advises Aleksunes. That way, when a new prescription comes in, your pharmacist can suggest how to fit it into your routine so you can remember to take all your medications at the right time — and in the right way.