What patients eat or drink can have enormous consequences on how a drug works. Some drugs are best taken on an empty stomach, whereas many more are advised to be taken with food – or even with a great deal of liquid. Some medicines even react with seemingly innocuous substances like coffee or milk. Medical professionals need to remain cognisant of these important food-drug interactions – many of which have significant clinical effects. Patients also need to be adequately counselled so as to know what to take and how to take it.

5 Common Food-Drug Interactions

Food and drink can have the following three effects on drug function:

  • They can prevent the drug from working
  • They can cause side effects to become better or worse
  • They can create a new, unintended effect

The reverse is also true, in that medicines have the capacity to affect the metabolism of various nutrients and minerals. Food and drink is, after all, only dietary chemistry and, like all chemistry, it has the capacity to react. Here, we’re going to list some important food-drug interactions – looking at what happens to the drug when it’s taken in the presence of a particular food or drink. The list is by no means intended to be exhaustive, but merely serves as an introduction to an increasingly important subject.

Important Food-Drug Interactions

Drugs Food Food-Drug Interactions
WARFARIN High-protein diet Raises serum albumin levels, decreases in international normalized ratio (INR)
  Vegetables containing vitamin k Interferes with effectiveness and safety of warfarin therapy
  Charbroiled Decreases warfarin activity
  Cooked onions Increases warfarin activity
  Cranberry juice Elevated INR without bleeding in elderly patients
  Leafy green vegetables Thromboembolic complications may develop
  Charbroiled Decrease warfarin activity
MONOAMINE OXIDASES Tyramine-containing food Hypertensive crisis
PROPRANOLOL Protein-rich food Serum level may increase
ACE INHIBITORS Empty stomach Absorption is increased
Grapefruit juice Increases bioavailability
ANTIBIOTICS Dairy products Calcium complexes with some antibiotics and prevents their absorption – reduced bioavailability
ACETAMINOPHEN Pectin Delays both absorption and onset
NSAIDS Alcohol Increases risk of liver damage or stomach bleeding
  Beverages c max and auc0-alpha significantly increased
THEOPHYLLINE High-fat meal and grapefruit juice Increases bioavailability
  Caffeine Increases risk of drug toxicity
ESOMEPRAZOLE High-fat meal Bioavailability was reduced
CIMETIDINE with food(any type) Increases bioavailability
ISONIAZID Plants, medicinal herbs, leanolic acid Exerts synergistic effect
CYCLOSERINE High fat meals Decreases serum concentration
ATORVASTATIN Grapefruit juice Increases toxicity – rhabdomyolysis risk
GLIMEPIRIDE With breakfast Absolute bioavailability
ACARBOSE At start of each meal Maximum effectiveness
MERCAPTOPURINE Cow’s milk Reduces bioavailability
TAMOXIFEN Sesame seeds Inducing regression of established mcf-7 tumor size but beneficially interacts with tamoxifen on bone in ovariectomized athymic mice
LEVOTHYROXINE Grapefruit juice Delays absorption

Note that alcohol should not be consumed with any drug, but some alcohol-drug interactions are more serious than others. Patients taking psychoactive substances – whether it’s SSRIs, anaesthetics, anticonvulsant drugs, or some analgesic preparations – are likely to exhibit worsening side effects if taken with alcohol. Respiratory depression is, for example, more likely in patients taking hypnotics (and many other drug classes).

Want to learn more about food-drug interactions? Join our member’s area today. There, we go through each major drug class – detailing what food-drug interactions you, as a healthcare professional, are expected to know.

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