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Food-Drug Interaction


How sure are you of your medications which you consume everyday are safe and effective just like how you want it to be? Do you feel better, same or even worse when you take them? You keep thinking to yourself that you’ve never missed a dose, but yet, the drugs are still failing to work due to unclear reasons. When this happens, you should start thinking of the factors influencing its failure and as a start, Food-Drug Interaction should come across your mind in an instance!


A drug interaction is actually defined as any modification caused by another exogenous chemical such as drugs, herbs and food in the diagnostic,therapeutic or other action of a drug in our bodies. It can happen when the food that you eat affects the ingredients in the medications that you are taking, preventing it to work the way it should be.

The significance of interactions between drugs has always been a highlight to healthcare professionals and their patients. However, little attention has been given to food-drug interaction despite how detrimental it can be to a person’s well-being or even his life.

Food-drug interactions can have profound influence on the effectiveness of the drug therapy as well as the adverse reaction profiles of various drugs. In other ways, it can also increase the therapeutic value of the drugs by improving the drug absorption or reducing its side effects.

Current Situation In Malaysia

Being a multi-ethnic Asian country we are predisposed to many types of food and herbal remedies which has been used centuries ago. The US Food & Drug Administration (FDA) mandates that only medicines have to be proven to be safe before being released to the market. Herbal products which are classified as dietary supplements do not fall under this category as long as it is not marketed under the indication of preventing diseases.

Most of the people around the world including Malaysians believe that herbs are harmless plants while not knowing that some drugs are derived from plants itself such as morphine, atropine and some chemotherapeutic drugs.

Due to this belief as well as the fear of confessing their practice to their healthcare professionals, patients fail to inform their history of taking herbals or supplements with their medications.

Types of Food – Drug Interaction

This interactions can occur with prescriptions drugs, over-the-counter drugs (OTC), herbal products and even dietary supplements.

There are 2 categories which are the nutrient-drug interaction and the herbal/supplements-drug interactions.

Nutrient-drug interactions take place when the consumed food gives an effect towards the medication. Factors such as timing of medication intake and type of food taken shall be emphasized to prevent harmful effects. Most common type of interactions are with alcohols, tyramine-containing food (such as tapai, chocolate, cheese) and caffeinated beverages (Refer Table 1).


of Drugs
Examples of
Drug (Brand Name)
Allergies Antihistamines Take without regard of food. Bioavailabilty decreases with apple, orange, grapefruit juice.
  • Diphenhydramine
  • Loratadine
  • Cetrizine
Arthritis/Pain Analgesics Take on empty stomach for rapid relief
  • Paracetamol
Arthritis/Pain Non-Steroidal Anti Inflammatory Drugs (NSAIDs) Take with food or milk to decrease stomach upset
  • Aspirin
  • Ibuprofen
Arthritis/Pain Corticosteroids Take with food or milk to decrease stomach upset
  • Prednisolone
Asthma Bronchodilators High fat meals may increase the amount of theophylline in the body, while high carbohydrate meals decrease it. Avoid eating / drinking large amounts of caffeine – containing food, drinks.
  • Theophylline
  • Salbutamol
Cardio-Vascular Disorders Diuretics Take on empty stomach/with milk to decrease stomach upset.
  • Frusemide
  • Bumetanide
  • Hydrochlorothiazide
Cardio-Vascular Disorders Beta Blockers Take with food to increase bioavailability.
  • Atenolol
  • Metoprolol
  • Propranolol
Cardio-Vascular Disorders Nitrates Take on empty stomach.
  • IsosorbideDinitrate
  • Nitroglycerin
Cardio-Vascular Disorders Angiotensin Coverting Enzymes Take on empty stomach. Ensure adequate fluid intake.
  • Captopril
  • Perindopril
  • Lisinopril
Cardio-Vascular Disorders Inhibitors (ACEi) Avoid salt substitutes.
  • Enalapril
Cardio-Vascular Disorders MNG-CoA Reductase inhibitors (Statins) Avoid grapefruit / related citrus. Avoid high fibre meals. Best taken before bedtime.
  • Atorvastatin
  • Simvastatin
Cardio-Vascular Disorders Anticoagulants Limit food high in Vitamin K such as broccoli, leafygreens, cauliflower as it produces blood – clotting substances that may reduce effectiveness of the drug. Vitamin E (400IU or more) may prolong clotting time leading to bleeding.
  • Warfarin
Infections Penicillin/Quinolones /Cephalosporins Take on empty stomach 1 hour before or 2 hours after unless it upsets stomach, take with food but not with dairy or calcium – fortified food.
Quinolone: Avoid caffeine as it increase excitability & nervousness
  • Penicillin:Penicillin V,
  • Quinolones:Ciprofloxacin,
  • Cephalo: Cephalexin,
Infections Macrolides May take with food if GI distress.
Avoid citrus food, carbonated drinks and citrus juices
  • Azithromycin
  • Erythromycin
  • Clathromycin
Infections Sulfonamides Take with food and at least with 8 ounces of water.
  • Sulfamethoxazole/
Infections Tetracycline Take with food and at least with 8 ounces of water. Avoid taking it with dairy products, antacids, vitamin supplements containing iron as it can interfere with drug’s effect.
  • Tetracycline
  • Doxycycline
Infections Nitromidazole May take with food to decrease GI distress.
  • Metronidazole
Infections Antifungals Take with food to increase absorption. Do not take itraconazole with citrus.
  • Fluconazole
  • Ketoconazole
  • Itraconazole
Mood Disorders Monoamine Oxidase (MAO) Inhibitors Do not take foods or alcoholic beverages containing tyramine (eg.cheese, tapai, soy sauce, tofu, bananas, raisins, caffeine) while taking this drug and for 2 weeks after discontinuation.
  • Selegiline
Mood Disorders Anti-Anxiety May take with food to decrease GI distress. Caffeine may cause excitability and lessen the anti-anxiety effect of the drug.
  • Alprazolam
  • Diazepam
Mood Disorders Antidepressant To be taken with or without food.
  • Sertraline
  • Fluoxetine
Stomach Conditions Histamine Blockers To be taken with or without food. Caffeine may irritate stomach.
  • Cimetidine
  • Ranitidine

Herbal/supplement-drug interactions occur when the public consume these preparations and causes unintended effects varying from allergic reactions to cardiovascular, hepatic, renal, neurological and dermatological toxic effects. The predisposition towards high doses of herbs or the length of intake together with medication (long term) can cause even more harmful outcomes. Common examples of herbal preparations or supplements which can interact with drugs are ginseng, turmeric, garlic, Gingko Biloba, ginger, Dong Quai, neem, tulasi and many more (Refer Table 2).


Herbs Supplements
Interacting Drug
Possible Effects

to stimulate adrenal gland which increases energy and reduce blood glucose

Warfarin May decrease drug’s effectiveness
Corticosteroids May potentiate drug and increase side effects
Antihypertensive May increase blood pressure
MAOIs May increase insomnia, headache, tremulousness
Gingko Biloba

for the treatment of dementia & to improve memory

Aspirin Bleeding
Warfarin Haemorrhage
Thiazide Hypertension

to lower blood pressure & cholesterol

Warfarin Increased effectiveness of warfarin, leads to bleeding

for nausea & bowel spasms

Warfarin Increased effectiveness of warfarin, leads to bleeding
Dong Quai

for menopausal symptom control

Warfarin May increase the effect of this drug which can lead to bleeding
St. John’s wort

a natural anti –depressant for mild to moderate depression.

Amitriptyline Worsen depression as it reduces concentration of the drug in the blood
Digoxin Decrease digoxin concentration leading to reduce efficacy of digoxin
Theophylline Worsen signs & symptoms of asthma as it reduces concentration of the drug in the blood
Oestrogen Causes breakthrough bleeding
Green Tea

as an antioxidant

Calcium Decreases calcium absorption
Warfarin Warfarin activity might be lowered due to high level of vitamin K in herb

as an anti inflammatory, to treat digestive and liver problems, skin diseases, wounds

NSAIDs May increase bleeding and gastrointestinal irritation
Warfarin, Aspirin May increase the effect of this drug which can lead to bleeding
Ranitidine,Omeprazole May increase production of stomach acid
AzadirachtaIndica (Neem)

antiseptic, antiviral, antipyretic, anti-inflammatory, anti-ulcer

Insulin May decrease glucose level further
Immunosuppressants (eg:Cyclosporine Azathioprine) May increase immune’s system which leads to decrease of medications efficacy.

for common colds, headache

Anticoagulants,antiplatelets May slow blood clot which leads to increase bleeding and bruising
Eurycomalongifolia (Tongkat Ali)

to stimulate male hormones, increase libido

Immunosuppressants May further weaken immune system

Mechanism Of Food – Drug Interaction

By knowing the possible mechanism involved during food-drug interaction, you can actually take safety measures to avoid the unwanted effects, thus ensuring you get all the benefits expected from the medications.

These mechanisms are categorized into 2 which are pharmacokinetic and pharmacodynamics mechanisms.

Several pharmacokinetic mechanisms may occur when there is an increase or decrease in:

  • Absorption of a drug into the body
  • Distribution of the drug within the body
  • Metabolism of the drug inside the body.
  • Elimination of drug from the body.

An additive activity of the drug due to food is a classic example of a pharmacodynamic interaction, for example, the anticoagulant effect of warfarin is enhanced by gingko and possibly many other herbs.

Consequences of Food-Drug Interaction

There are 2 types of implications towards our body which can be beneficial or detrimental. The latter one is the greatest concern as it can reduce the desired effect expected from a drug or even increase the adverse effects.

When the absorption of drugs increases due to intake of food, these drugs are taken together in order to increase their concentration in the body. Conversely, when its absorption is reduced by food, the drug is taken on an empty stomach.

On the other hand, foods that reduce the absorption or increase the metabolism or elimination of the drugs tend to reduce the effectiveness of the drug. This may lead to therapy failure and may increase the risk of side effects. Therefore it is wise to know the possible effect of the interactions.( Refer Table 2).

Medication Safety Measures

9 tips to avoid food-drug interaction:

  • Always READ the prescription LABELS and product leaflets (directions, warnings, interaction precautions) printed together with the medication container.
  • It is very important to FOLLOW INSTRUCTIONS given on how to take the drugs safely by your healthcare providers.
  • Take medication with a full glass of PLAIN WATER. Do not mix with hot drinks as the heat will destroy the effectiveness of some drugs.
  • DO NOT STIR medication into your food unless advised otherwise.
  • DO NOT take herbals remedies or supplements the SAME TIME you take your medications.
  • NEVER consume ALCOHOL together with your medications.
  • ALWAYS be sure to INFORM you doctors and pharmacists about all the medications as well as the herbs/supplements that you are taking.
  • INFORM healthcare providers about any changes in lifestyle recently (exercise, diet, alcohol intake).
  • If you have any questions or concerns about possible drug interactions, always APPROACH and consult your DOCTOR/PHARMACIST.


The effectiveness of a drug is a very important concern to ensure your diseases are well controlled or even cured. Therefore, always remember of any possible food-drug interaction that may occur when you are consuming them. Be sure to follow the useful tips to avoid unnecessary effects and to get the best out of your medication. Do not be hesitant to approach your healthcare providers, as we are always here to make a better YOU!

Last reviewed : 23 April 2014
Writer : Puteri Juanita bt. Zamri
Reviewer : Che Pun bt. Bujang