Food and interference with medications

Content

What can food-drug interactions cause?

The interaction between foods and medications can cause:

Medications to work faster or slower, better or worse;
Cause a side effect from a medicine to get worse or better;
Cause a new side effect, or;
Reduce or enhance the absorption of certain nutrients in food.

What foods can cause food-drug interactions?

Any type of food is capable of causing food-drug interactions, depending on the following factors:

Type and dosage of medication(s);
Timing of intake of food - for example, on an empty or full stomach;
An individual's age, weight and gender;
Existing medical conditions, and;
Use of vitamins, herbal or dietary supplements.

Importantly, caffeine and alcohol can also cause food-drug interactions.

Does it matter if I take medicine on a full or empty stomach?

For certain medicines, taking food on a full or empty stomach can have a significant effect on its function. This is because the digestive process that breaks down the food we eat, can also affect medicines. Unfortunately, there is no general rule on when is the best time to take medicines. This differs greatly between medicines. Therefore, it is important to follow the directions on the medicine label, or ask your doctor or pharmacist for advice.

Below are explanation of common instructions found on medicine labels.

Instruction: Take on an empty stomach.
Explanation	Examples
Take 1 hour before meals or 2 hours after meals.	Some antibiotics don't work as well if taken with food.
Instruction: Don't take with certain foods.
Explanation	Examples
Don't take within 1 hour before or 2 hours after meals containing the specified food to avoid.	Some osteoporosis medications don't work well when taken with calcium-rich foods, such as milk, yoghurt and calcium supplements.
Instruction: Don't eat certain foods at all.
Explanation	Examples
Avoid taking the specified food altogether while on the medication.	Some cholesterol-lowering medicines, heart medicines and several other common medicines are affected by grapefruit juice. Even a small amount of grapefruit juice can have a significant effect on these medicines.
Instruction: Eat consistent amounts of certain foods.
Explanation	Examples
Don't change your diet during the course you are on the medication.	Warfarin (known as Coumadin or Marevan), a blood-thinning medicine, is affected by vitamin K in the diet. Rather than avoid vitamin K-rich foods altogether (such as green vegetables, egg yolks, chickpeas or lentils), it is preferable to eat a consistent amount of these foods. This will allow your doctor to prescribe a predictable dose of warfarin, which prevents unwanted complications.
Instruction: Take with meals.
Explanation	Examples
Take at meal times or up to half an hour before or after meals.	Non-steroidal anti-inflammatory drugs (NSAIDs) that are commonly used as pain-relief medications (such as ibuprofen or aspirin), can cause indigestion and stomach ulcers if taken on an empty stomach.
Instruction: Take at the same time, each time.
Explanation	Examples
Take at the time directed by your doctor or pharmacist. Generally, even if not advised, taking medicines at a set time each day also helps you remember to take them.	Frusemide, a heart medication, is taken at set times of the day (morning and/or lunchtime) to reduce unnecessary side effects, such as frequent urination at night.

Does it matter if I take medicine with alcohol?

In general, alcohol tends to affect most medicines. This is because both alcohol and most medicines are broken down by the liver. Therefore, alcohol competes with these medicines leading to:

The medicines working faster or slower;
Increased or new side effects, or;
Alcohol lasting in your system longer.

In most cases it is best to not take medicines with alcohol. Take medicines either one hour before drinking alcohol or once alcohol is no longer in your system.

Does caffeine affect the medicines I take?

Caffeine, which is the active ingredient in coffee, but also found in tea, many soft drinks and even chocolate, can interact with certain medicines. In fact, caffeine is deliberately added to some prescription and over-the-counter medicines to treat tiredness and improve the effect of some pain-relief medicines. However, studies have shown that drugs like antidepressants, thyroid medicines and osteoporosis drugs can be affected by coffee. The absorption of osteoporosis and thyroid medicines can be reduced by coffee, whereas some antidepressants, antibiotics and certain asthma drugs can increase caffeine's effects, causing a rapid heart rate and a jittery feeling. Usually, moderate intake of coffee is generally safe (less than four cups per day). However, it is best to discuss this with your doctor or pharmacist if you are concerned.

Common food-drug interactions

The following is a list of conditions for which food and drug interactions are common. It is not complete and is intended as a guide only. Always read the label and speak to your doctor and pharmacist before trying any new medications or changing your dosage.

Condition	Medicine
Allergies	Antihistamines are a class of medications commonly used to treat allergies. There is a range of antihistamines, some of whom cause drowsiness.
Examples	Interactions
Loratadine Cetirizine Fexofenadine	Alcohol can interact with antihistamines, making you even drowsier.

Condition	Medicine
Hypothyroidism	Thyroid hormone replacement.
Examples	Interactions
Thyroxine	Levothyroxine is best taken on an empty stomach in the morning, at least 30-60 minutes before eating.