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Drug interactions

Published on March 8, 2024 at 8:00 / Updated on March 26, 2024 at 8:00

A drug interaction is a change in the effect of a drug when it is taken along with another substance. Among others, this substance could be:

  • Another medication
  • A natural health product
  • A dietary supplement (e.g., a vitamin or mineral)
  • A food item (e.g., grapefruit)
  • A tobacco product (e.g., cigarettes)
  • Alcohol
  • Cannabis


A drug interaction can result in the following:

  • Decreased effectiveness of a treatment
  • Increased side effects of a treatment

Developing of a drug interaction

When you take a drug, it immediately embarks a complex journey throughout the human body. Drug interactions can occur at many points throughout this journey. As a drug passes through the human body, it goes through the following stages:

  • Absorption - The drug enters the bloodstream
  • Distribution - The drug travels to different parts of the body
  • Metabolism - The drug transforms into a different molecule
  • Elimination - The drug is evacuated from the body

Taking a substance that affects any of these steps throughout the journey of a drug can lead to a drug interaction. For example, taking iron (a mineral) may mitigate the passage of certain antibiotics into the bloodstream. Treating an infection with such antibiotics could therefore fail, because they will not be able to enter the bloodstream in sufficient amounts.


Certain segments of the population are at greater risk of drug interactions. This includes people who are taking multiple medications or who have multiple medical conditions.

Issues with the liver or kidneys may cause a drug to stay in the body for longer due to inadequate elimination. When a drug stays in the body for longer, more side effects may occur, and the drug has a higher likelihood of interacting with other drugs.

With age, certain functions of the human body become less efficient. For example, the liver functions less well, and the same is true for the kidneys. Older people tend to have more health problems and are often on multiple medications. All of these factors put them at greater risk for drug interactions.


To avoid adverse consequences of a drug interaction, you can do the following:

  • Talk to your pharmacist before taking a new product, such as:
    • Medication, whether or not it is prescribed
    • Natural health products
    • Dietary supplements (e.g., a multivitamin)
  • Get all of your medications from the same pharmacy
  • Maintain an updated list of your medications
  • Tell your health care professionals about the medications you are taking

Your pharmacist plays a very important role when it comes to preventing drug interactions. In fact, potential drug interactions are verified when your file is assessed by the pharmacy. This assessment is done whenever a prescription is renewed or whenever you fill a new prescription or purchase a non-prescription drug.

Your pharmacist may then suggest a dosage change, recommend that you take your medication at a different time of day, or even recommend a new medication altogether. Your pharmacist is there to ensure that all of your medications are taken safely.

The drugs and pharmaceutical services featured on the website are offered by pharmacists who own the affiliated pharmacies at Familiprix. The information contained on the site is for informational purposes only and does not in any way replace the advice and advice of your pharmacist or any other health professional. Always consult a health professional before taking or discontinuing medication or making any other decision. Familiprix inc. and the proprietary pharmacists affiliated with Familiprix do not engage in any way by making this information available on this website.