Six food and medication combinations to avoid

Timing is everything. Find out how what you're eating, and when, could adversely interact with your meds. Print off an easy-to-navigate chart.

Woman eating grapefruit with a spoon

Photo: Getty Images

Not surprisingly the combination of certain foods and your medication(s) can often affect how the drug is broken down, absorbed or metabolized in your liver. But many of us may not know the wrong combinations could mimic the drug’s action and exaggerate its effect. So whether you’ve just started a new medication, are experiencing side effects or suddenly find that what you’re taking isn’t working effectively, I suggest following these steps to ensure your prescriptions are consumed away from the most common offending interactions:

1. Cut out the caffeine
Period of sensitivity:
1 hour
Your morning cup of java may be causing more of a problem than you think, particularly if you consume it close to taking thyroid medication.

In one small study, when a T4-based medication was swallowed with coffee/espresso, it lowered the average and peak incremental rise of thyroid hormone by up to 36 percent. If you take your medication upon rising then you should wait 45-60 minutes before your first cup of coffee.

However, that doesn’t mean you should switch to black tea. Research shows that it too can have an inhibitory effect on how certain drugs are metabolized by the liver.

Bottom line: To play it safe, stick to drinking water with your meds.

2. Ease off on alcohol
Period of sensitivity:
Duration of medication/supplements
You’ve probably seen the warnings on your prescription bottle and these are there for good reason. Alcohol can affect antidepressants, antihistamines, sleeping pills, sedatives, and even some antibiotics. Mixing common antibiotics with alcohol can increase the likelihood of more severe side effects including, headaches, cramps, nausea and vomiting.

Meanwhile, a mix of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) with alcohol can damage the gastric mucosal barrier and increase the risk of gastrointestinal bleeding. How many times do people take these to avoid a hangover before bed?

Bottom line: Sometimes even the type of alcohol matters. A study published in the Journal of Agricultural and Food Chemistry found that more bitter-tasting beers reduced the effect of the cancer drug Tamoxifen, when compared with beers that were less hopped.

 3. Watch your dairy intake
Period of sensitivity:
1-4 hours
Dairy is known to affect the absorption of iron supplements; however both of them impact the absorption of certain medications, particularly for thyroid. If you are taking all three, you may need to do some creative planning – such as taking your thyroid first thing in the morning, iron at dinner (preferably with digestive enzymes and vitamin C to aid absorption) and calcium at bedtime (also preferably in combination with magnesium glycinate). The calcium in dairy has also been found to interfere with some antibiotics (such as tetracyclines and ciprofloxacin) because it binds to the antibiotics in the stomach and to form an insoluble compound. In turn, you get less of the active compound circulating in your bloodstream. In this case, often separating it by 1-2 hours is sufficient. You may just need to have your prescription in one hand and a diet diary in the other to ensure there are no unwanted interactions.

4. Don’t fill up on fibre
Period of sensitivity:
2 hours
Fibre is probably the most common potential food interaction. It slows the rate that the stomach empties, including all that’s in it — medications and all — leaving you with a lower dose than desired. I’ve had patients on thyroid medication experience a dip in energy that corresponded with a boost in their fibre intake because they were unknowingly letting these two worlds collide. In the aforementioned study on thyroid medication versus caffeine, they also included bran as a test agent and — not surprisingly — found it to interfere with thyroid absorption.

Bottom line: To avoid any issues simply take any fibre supplements 2 hours away from any medications. Or, for those on thyroid medication, another option is to take the medication before bed, and move your iron to lunch and your calcium to dinner to avoid the fibre/calcium/iron conundrum.


5. Steer clear of grapefruits
If you like to start off your morning with eggs and a side of grapefruit you may want to rethink your breakfast. Grapefruit (juice and supplements) can interact with more than 50 prescription drugs — from birth control and heart medications to allergy and immunological drugs — by inhibiting an enzyme in the intestine that breaks down the drug. In turn you end up getting a higher dose than anticipated which can substantially increase the likelihood of side effects. Some types of oranges can also have this affect.

6. Herbs and vitamins can interact too
Many common supplements can decrease the effectiveness of your medication. Common ones include garlic, valerian, gingko, licorice root, echinacea and St. John’s Wort. While all this may seem confusing, it doesn’t have to be a guessing game.

Bottom line: I recommend you create a daily vitamin and medication dosing sheet with the assistance of your team of health practitioners, including your ND and pharmacist. Your dosing schedule should list what medications and vitamins are taken at what time to avoid interactions as well as maximize absorption.

Here’s a handy reference guide if you’d like to complete a quick check of your possible interactions*:

Drug Food Increase Drug Effect Decrease Drug Effect
Some statins
(eg, Lipitor, Zocor, Mevacor, Advicor)
Grapefruit, pomegranate, and cranberry juices


(MAO inhibitors)
Chocolate and other foods containing tyramine


Allergy medications (eg, Allegra) Black pepper


Potentially all drugs metabolized by P450 liver enzymes Black tea


Cancer drugs
(eg, tamoxifen)


Anticlotting agents
(eg, Plavix)
Fatty fish


(hypertension medications)


Blood thinners
(eg, Coumadin)
Leafy greens


(hypertension medications)
Natural licorice


(eg, Cipro, tetracycline)
Milk and calcium-fortified juices


 *Source: http://www.todaysdietitian.com/newarchives/121610p26.shtml

Natasha Turner, N.D. is a naturopathic doctor, Chatelaine magazine columnist, and author of the bestselling books The Hormone Diet and The Supercharged Hormone Diet. Her newest release, The Carb Sensitivity Program, is available across Canada. She is also the founder of the Toronto-based Clear Medicine Wellness Boutique. For more wellness advice from Natasha Turner, click here.

Get Chatelaine in your inbox!

Our very best stories, recipes, style and shopping tips, horoscopes and special offers. Delivered a couple of times a week.