Medicines and meals: Before or After food

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Food and its constituents may have a significant effect on both the rate and extent of absorption of drugs after oral administration. Understanding the effect of meals on medicines enables health professionals to advise patients about taking medicines with or without food. Co-administration of drugs with food generally delays drug absorption. However, meals may have a variable effect on the extent of absorption – depending on the characteristics of the meal, the drug and its formulation. Some drugs have strict guidelines about when they should be taken in relation to meals. Generally, patients should be advised to take their medicines consistently at the same time with respect to meals.

Understanding the possible clinical implications of taking medicines with or without a meal is important for achieving quality use of medicines. Although the effect of food is not clinically important for many drugs, there are food-drug interactions which may have adverse consequences. Often these interactions can be avoided by advising the patient to take their medicines at the same time with respect to meals.

The effect of food on absorption

The effect of food on absorption refers to how the presence of food in the digestive system can influence the absorption of nutrients, medications, and other substances. Food can affect absorption in several ways:

  1. Enhanced Absorption:
    • Some nutrients are absorbed better in the presence of food. For example, the absorption of fat-soluble vitamins (A, D, E, and K) and certain minerals like calcium and iron is enhanced when consumed with food containing fats or acids.
  2. Delayed Absorption:
    • Certain medications may have delayed absorption when taken with food. This delay can be intentional, as it may help reduce stomach irritation or slow down the release of the medication for better efficacy or tolerance.
  3. Decreased Absorption:
    • Some substances may have reduced absorption when taken with certain types of food or beverages. For example, the absorption of certain antibiotics or minerals like iron can be inhibited by consuming them with foods containing compounds like calcium or tannins found in tea.
  4. Interaction with Gastric Emptying:
    • Food can affect the rate at which the stomach empties its contents into the intestines, thereby influencing the absorption rate of nutrients and medications. Foods high in fiber, fat, or protein tend to slow down gastric emptying, while liquids and low-fiber foods may speed it up.
  5. Interaction with Enzymes and pH:
    • The presence of food can alter the pH and enzyme activity in the digestive tract, which can affect the breakdown and absorption of nutrients and medications. For example, stomach acid helps break down proteins and activate certain enzymes, facilitating their absorption.
  6. Drug-Food Interactions:
    • Some medications can interact with specific foods, affecting their absorption, metabolism, or efficacy. These interactions may be due to competition for absorption sites, changes in pH affecting drug solubility, or interference with drug metabolism.

Understanding the effect of food on absorption is crucial for optimizing nutrient intake and medication efficacy while minimizing potential interactions or adverse effects. It’s often recommended to follow specific instructions provided by healthcare professionals regarding the timing and conditions for taking medications and supplements in relation to meals.

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Studying the effect of food

Studying the effect of food on various aspects of human health and physiology is a complex and multifaceted endeavor that involves interdisciplinary approaches combining nutrition, biochemistry, physiology, pharmacology, and other fields. Researchers employ several methods to investigate how food influences absorption, metabolism, and overall health outcomes:

  1. Clinical Trials: Clinical trials involve studying human subjects to evaluate the impact of different dietary interventions on health parameters. These trials may include randomized controlled trials (RCTs) where participants are assigned to different diet groups to assess the effects of specific foods, nutrients, or dietary patterns on absorption, metabolism, and health outcomes.
  2. Observational Studies: Observational studies, such as cohort studies and case-control studies, analyze the relationship between dietary patterns, nutrient intake, and health outcomes in large populations over time. These studies can provide valuable insights into long-term effects of food on absorption and health.
  3. In Vitro Studies: In vitro studies involve experiments conducted outside the living organism, often using cell cultures or isolated tissues, to investigate mechanisms of nutrient absorption and metabolism. These studies can help elucidate cellular and molecular processes underlying the effects of food components on absorption.
  4. Animal Studies: Animal studies are used to investigate the physiological and metabolic effects of different diets and food components under controlled conditions. Animal models provide valuable insights into mechanisms of absorption, nutrient metabolism, and the impact of diet on overall health.
  5. Nutrient Bioavailability Studies: Nutrient bioavailability studies assess the extent to which nutrients from food are absorbed and utilized by the body. These studies may involve measuring blood levels of specific nutrients or using stable isotopes to track nutrient absorption and metabolism.
  6. Imaging Techniques: Advanced imaging techniques, such as magnetic resonance imaging (MRI) and positron emission tomography (PET), can be used to visualize physiological processes in real-time, providing insights into the dynamics of nutrient absorption and metabolism in humans.
  7. Metabolomics and Molecular Techniques: Metabolomics and molecular biology techniques allow researchers to analyze changes in metabolites, gene expression, and protein levels in response to dietary interventions. These approaches help identify biomarkers of nutrient absorption and metabolism and elucidate molecular mechanisms underlying the effects of food on health.

The product information approved by the Therapeutic Goods Administration is the main source of information about the possible effects of food on drug absorption. This information is generally derived from a ‘food effect study’ that is conducted during drug development. Typically, this involves a randomised cross-over single dose pharmacokinetic study in healthy people.

They take the drug of interest after an overnight fast and also after a standard high fat breakfast. This design is meant to examine the effect of food under ‘extreme’ conditions. Unfortunately, a volunteer eating a high fat meal does not necessarily reflect the circumstances of the patients who will take the drug. Dosing recommendations with respect to food derived from these studies may therefore not provide the best guide to the actual impact of food on drug absorption.


Meals may have variable and often unpredictable effects on drugs via a range of mechanisms. By understanding and appreciating the clinical consequences of these effects health professionals can provide advice about the appropriateness of ingesting medicines with respect to the times and the composition of meals. The provision of timely and appropriate advice about the possible effects of meals on medicines and the importance (or lack) of the timing of meals and medicines is an important issue impacting on the quality use of medicines.


  1. Birkett DJ. Pharmacokinetics made easy. 2nd ed. Sydney: McGraw-Hill; 2002.
  2. Coxeter PD, McLachlan AJ, Duke CC, Roufogalis BD. Herb-drug interactions: an evidence based approach. Curr Med Chem 2004;11:1513-25.
  3. Fugh-Berman A. Herb-drug interactions. Lancet 2000;355:134-8.

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