Feature Articles


Avoiding Drug Interactions

How to safely take prescriptions and reduce interactions with food, alcohol and OTC drugs.
By Frieda Wiley, PharmD, CGP, RPh
Published: August 20, 2015
Last updated: June 16, 2016

Many of us are getting better at asking questions about how the drugs we are prescribed work or what their side-effects might be. And yet we often remain uninformed, or at least unsure, of how the drugs we take interact with the food we eat, over-the-counter drugs we also take, or the alcohol we (may) drink.

Nearly half of US residents took at least one prescription drug within a 30-day period in 2012, according to the CDC. Americans also rely heavily on over-the-counter products, as the average household will spend $340 this year on these often cheaper, non-prescription remedies, says the Consumer Healthcare Products Association (CHPA). And yet, despite being a highly medicated society, the overwhelming majority of Americans do not seek advice about how to take their medications properly — frequently resulting in undesirable consequences like severe side effects, dangerous drug interaction, inability to manage an illness, or even, occasionally, death. Drug interactions are often responsible for some these unwanted reactions, and that risk obviously rises the more drugs a person takes.

Here is a guide designed to clear up some commonly held misconceptions about drug interactions involving food, OTC drugs and alcohol.

Food Plus Prescription Drugs

What you eat and drink affects how the drugs you take work in your body, in a couple of ways. First, certain foods may interfere with a particular drug’s active ingredients, rendering it less effective. Second, foods can make a drug’s side effects more pronounced. Two common food-drug interactions are here:

Blood Thinners and Green Vegetables

greensVsBloodThinnerMany people believe that they should avoid all green vegetables if they are taking blood thinners. This is simply not true. Green vegetables don’t interact with all blood thinners, but they just happen to interact with the most commonly prescribed blood thinner in history, warfarin (Coumadin or Jantoven).

“It’s a myth that warfarin patients should stay away from these foods,” says Devon Trumbower, PharmD, BCPS, an internal medicine clinical pharmacist with the Christiana Care Health System in Wilmington and Newark, DE. “Green veggies like spinach, kale, and broccoli are high in vitamin K, which can antagonize warfarin’s ability to anti-coagulate or ‘thin’ the blood,” she notes. A more accurate recommendation for green vegetables and blood thinners is to be consistent with how much high-vitamin-K-containing foods you eat while on warfarin. That means, for example, about a serving or so a day, rather than going on a kick of an all-veggie diet one week, and then eating no green veggies the following week.

So while the amount of vitamin K in your food may interact with your warfarin, it doesn’t mean you have to avoid green vegetables altogether. But, what it does mean is that you might:

  • Want to discuss adding leafy greens to your diet with your doctor
  • Be referred or ask your doctor for a referral to an anti-coagulation clinic
  • Need a dose change if you’ve altered your diet, which means you may have to get your blood checked a few times until your doctor pinpoints your new dose

Maybe (with your doctor’s okay) you really can have your greens and eat them too!

Next: Grapefruit and many drugs >>

Frieda Wiley, PharmD, CGP, RPh

Frieda Wiley, PharmD, CGP, RPh

Frieda Wiley is a medical writer and consultant pharmacist who calls the serene Piney Woods of East Texas home. Her work has appeared in Arthritis Today, Diabetes Self-Management, Everyday Health, and Next Avenue. She also develops content for medical students and allied healthcare professionals.

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