Home / Blog / All You should Know About Drug-Food Interaction And Pharmaist Role.

All You should Know About Drug-Food Interaction And Pharmaist Role.

Saroj Poudel Saroj Poudel | August 21, 2019
All You should Know About Drug-Food Interaction And Pharmaist Role.
According to WHO, A change in a drug's effect on the body when the drug is taken together with certain foods. A drug-food interaction can delay, decrease, or enhance absorption of a drug. This can decrease or increase the action of the drug or cause adverse effects.

Both food and drugs taken by mouth must be absorbed though the lining of GIT. So, when both were taken concurrently, the food present in the lining of tract may reduce the absorption of drug and interaction can happen. Such interaction can be avoided by taking the drug one hour before or two hours after eating. So, it’s a responsibilities of pharmacist that they should counsel to their patient as some medicine needs to be taken in empty stomach and some with food.

Large amount of green leafy vegetables, broccoli, spinach are high in vitamin K (promotes the formation of blood clots) can counteract the effects anticoagulant drugs such as heparin, warfarin etc. Certain soluble fibres and pectin rich foods (apples, guavas and citrus fruits)may reduce the absorption of NSAIDs (Acetaminophen).

Dietary supplements such as vitamin, mineral, amino acid that are intended to supply supplement to the body may interact with both prescription as well as over-the-counter drugs. Theophylline, a medication administered to treat asthma contains xanthine’s, which are also found in tea, coffee, chocolate and other sources of caffeine. Consuming large amounts of these substances while takingtheophylline, increases the risk of drug toxicity. So, People who take dietary supplements should inform their doctors and pharmacists so that interactions can be avoided simply by taken at different times; rather than eliminating one or the other from the diet.

Alcohol is a drug that interacts with almost every medication, especially antidepressants and other drugs that affect the brain and nervous system. For example, taking alcohol with metronidazole can cause flushing, headache, palpitations, nausea and vomiting.Hence, pharmacist should give the information about such interactions to the patients to avoid the toxicity.

Table: 1 Example of drug-food interaction that increase their absorption.



Pharmacist Counselling Points to patient.


Drug is lipid soluble, enhanced absorption with high- fat foods.

Take with high- fat foods. Combination with alcohol may cause flushing and fast heart rate.

Hydralazine, Labetalol, Metoprolol, Propranolol

Food may reduce first-pass extraction and metabolism.


Take with food


Delayed gastric emptying permits dissolution and absorption, bile may solubilize the drug.


Take with food

Carbamazepine, Phenytoin

Increased bile production, enhanced dissolution and absorption.

Take with food


Table: 2 Example of drug-food interaction that decrease their absorption



Pharmacist Counselling Points to patient.


Absorption is decreased when it is taken with food, resulting in a 43% reduction in bioavailability.

Should be taken half an hour after food.


When taken with high –fats food, may cause a sudden release of theophylline (dose dumping), resulting in increased theophylline concentrations and hence possibly toxicity.

Should not be taken with high-fats diet food


High pectin foods act as adsorbent and protectant

Take on empty stomach if not contraindicated or 1 hour after food.


High–fibre, high–pectin foods slow down the absorption of digoxin and make it less effective.

Take drug same time with relation to food, Avoid taking with high-fibre foods (Such as brown bread, cereals, fruit, vegetables and pulses).

Should be careful with salt substitutes.


Blood-thinning drugs interfere with vitamin-k dependent clotting factors. Taking with vitamin-k rich foods can decrease the ability of blood-thinners to prevent clotting.

Should not be taken with vitamin-k rich products.


Glipizide begins working in approximately 30 minutes to an hour. Since this drug increases insulin secretion, it is recommended that you should take it half an hour before meals to reduce the risk of hypoglycaemic episodes.

Affects blood glucose; more potent when taken half hour before meals.


Food raises gastric pH preventing dissolution and absorption.

Take on empty stomach if tolerated.

Tyramine rich food should be avoided while taking isoniazid. (Cheeses, wines, beer etc.)

Levodopa, Methyldopa

Drug competes with amino acids for absorption transport.

Avoid taking drug with high–protein foods.


May form chelate with calcium or iron.

Avoid taking with dairy products or iron–rich foods or supplements.


Binds with calcium ions or iron salts forming insoluble chelates.

Take one hour before or two hr after meals; do not take with milk.


Table 3: Examples of specific counselling on some drug-food interaction


Counselling points







MAO Inhibitors





Reduce appetite and can lead to excessive weight loss.


A low-salt diet increases the risk of lithium toxicity; excessive salt reduces the drug's efficacy.


Foods high in tyramine (aged cheese, processed meats, legumes, wine and beer among others) can produce a hypertensive crisis.


Many foods, especially legumes, meat, fish and foods high in Vitamin C, reduce absorption of the drugs.






Sleeping pills and Tranquilizers



Increase the risk of anaemia and nerve problems due to deficiency of folates and other vitamin B.

Patient should not drink alcohol or use other CNS depressant drugs while taking phenobarbital.


Never take with alcohol. Caffeine increases anxiety and reduce drug's effectiveness.


ACE inhibitors


Alpha blockers


Beta blockers



Potassium sparing diuretics


Antiarrhythmic drugs




Take on an empty stomach to improve the absorption of the drugs. Avoid food high in potassium, such as bananas.


Take with liquid or food to avoid excessive drop in blood pressure.


Take on an empty stomach; food, especially meat, increases the drug's effects and can cause dizziness and low blood pressure.


Unless a doctor advises otherwise, don't take diuretics with potassium supplements or salt substitutes, which can cause potassium overload.

Avoid caffeine, which increases the risk of irregular heartbeat.


Avoid taking with milk and high fibre foods, which reduce absorption, increases potassium loss.

Asthma Drugs





Avoid caffeine, which increase feelings of anxiety and nervousness.


High protein diet reduces absorption. Caffeine increases the risk of drug toxicity.

Cholesterol Lowering Drugs



Increases the excretion of folate and fat soluble vitamins.

Heartburn and Ulcer Medications



Cimetidine, Famotidine, Sucralfate


Interfere with the absorption of many minerals; for maximum benefit, take medication one hour after eating or empty stomach.


Avoid high protein foods, caffeine and other items that increase stomach acidity.

Hormone Preparations

Oral contraceptives





Thyroid drugs


Salty foods increase fluid retention. Drugs reduce the absorption of folate, vitamin B6 and other nutrients; increase intake of foods high in these nutrients to avoid deficiencies.

Salty foods increase fluid retention. Increase intake of foods high in calcium, vitamin K, potassium and protein to avoid deficiencies.


Iodine-rich foods lower the drug's efficacy.


                           Mineral Oils                            


Overuse can cause a deficiency of vitamins A, D, E, and K.







Always take with food to lower the risk of gastrointestinal irritation; avoid taking with alcohol, which increases the risk of bleeding. Frequent use of these drugs lowers the absorption of folate and vitamin C.

Increase fibre and water intake to avoid constipation.


Sodium alendronate


Fenofibrate, mebendazole, isotretinoin, tamsulosin, carbamazepine and labetalol.





The absorption of alendronate is impaired by food. It should be taken with plain water and nothing else should be consumed for at least 30 minutes.


Drugs that will be better absorbed when taken with food.


Patients taking digoxin should avoid taking bran fibre, pectin-containing foods such as apples or pears, or fibre containing, bulk-forming laxatives at the same time, since these agents may bind to the digoxin, decreasing its absorption.



  • Grapefruit juice (Cytochrome P450 3A4)
  • Well known food-drug interactions (Grapefruit juice and Statins)
  • Grapefruit juice inhibits cytochrome P450 3A4 enzyme and increase blood level of drugs, (atorvastatin, simvastatin, lovastatin)
  • Patients are at risk of statin-related side effects; muscle toxicity (myalgia, myopathy, or rhabdomyolysis)
  • Calcium channel blockers are popular drugs that also interact with grapefruit juice; (Amlodipine, nifedipine, nicardipine as well as Verapamil) and may increase the risk of orthostatic hypotension.
  • Oral contraceptivesare also affected by grapefruit juice; their serum levels increase only modestly when grapefruit juice is used concomitantly.
  • Tricyclic antidepressants; (clomipramine) is considered to be the well-documented drug of this class to interact.
  • Diazepam (Valium), temazepam (Restoril), and midazolam (Versed) are interacting agents of the benzodiazepine class that have increased concentrations and central nervous system depressant effects with grapefruit juice.1,3  However, other benzodiazepines (e.g., lorazepam, oxazepam) do not appear to be affected.Grapefruit juice doubles the oral systemic effects of budesonide (Entocort), increasing the risk of the already prevalent glucocorticoid effects.3 Buspirone levels and carbamazepine levels are increased with concurrent administration of grapefruit juice.1 Although ziprasidone levels can be elevated by concurrent consumption of grapefruit juice, other atypical antipsychotics do not appear to be affected.3


Role of Pharmacist in Prevention of Drug-Food Interactions:

Pharmacist plays an important role in monitoring for potential interactions and advising patients regarding food and beverages which may alter the drug mechanism.

  • It is important for pharmacist to provide information to patients on when to take their medications in relation to food intake.
  • Pharmacist need to aware of food-drug interaction which may be delayed, decreased or enhanced absorption of the drug.
  • Food delay the bioavailability of drugs and sometime patient may not get full therapeutic benefit of the medication.
  • According to JCAHO (The Joint Commission on the Accreditation of Healthcare Organizations), Pharmacist need to call the prescriber whenever the potential for drug-food interaction exists and document the communication and follow-up action on prescription or order form and counsel patient regarding potential interactions before their hospital discharge.

Counselling Point:

  • Patient need to take medication with full glass of water.
  • Pharmacist should inform to patient to read properly about direction, warning and precautions printed on all medication label and package inserts,
  • Don’t take vitamins and minerals supplements at the same time to your medicine.
  • Don’t drink alcohol with your regular prescribed medicine.
  • Don’t stir medicine into your food or take capsule apart unless your doctor tells you to.
  • Be sure to tell your physician and pharmacist about all medications you are taking.
  • Suspected medicine need to be taken at different times relative to foods
  • During pregnancy and nursing always consult a physician or pharmacist before taking any medicine.
  • Check with a doctor or pharmacist for the proper way and time to take medication.


Dr.Saroj Poudel

(Clinical Pharmacist)

Annapurana  Pharmacy P. Ltd.

+977 9851149866 +977 9851149866 +977 9851149866

Annapurna Pharmacy P. Ltd. announce easy online services to the customer for ordering medicine with home delivery services at fair price.