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SafeMedicationUse Newsletter

Preventing Harm from Drug–Food Interactions


Some medicines may affect how other medicines work. Certain foods, drinks, and dietary supplements can also affect how your medicines work. These "drug-drug interactions" and "drug-food interactions" may cause your medicines to become less effective or increase the risk of side effects. As a result, you may experience harmful effects.

It might seem obvious that interactions can occur between 2 medicines. It is important to know that medicines can also interact with food products. recently received a report from a consumer who experienced a drug-food interaction.

The consumer had been taking 1 tablet of indapamide in the morning. Indapamide is a medicine used to control high blood pressure. Later, the consumer began the habit of enjoying a smoothie prepared with psyllium husk, a dietary supplement rich in fibre, right after taking her medicine. During a follow up visit with her doctor, her blood pressure was found to be higher than before. To lower her blood pressure, the doctor increased the indapamide dose to 2 tablets every morning.

When the consumer purchased a new bag of psyllium husk, she noticed that the instructions said not to consume it within 2 hours of taking medicines. From then on, she made sure to wait at least 2 hours after taking her indapamide before drinking her daily smoothie. Not long afterward, her blood pressure became low, and she felt very dizzy.

The consumer began to suspect that her habit of drinking a smoothie after taking her medicine had likely caused the problems with her blood pressure. This was confirmed during a visit to her cardiologist. Psyllium husk can affect how much medicine the body absorbs. When the consumer first started drinking a daily smoothie, she had it right after taking her morning indapamide. The psyllium husk in the smoothie interfered with the absorption of her morning indapamide. As a result, the consumer needed a higher dose of the medicine to control her blood pressure. Then, when she began following the directions on the psyllium product, the absorption of indapamide went back to normal. With normal absorption, the dosage of 2 tablets of indapamide was too high. As a result, her blood pressure became too low.

Consumers can play a role in preventing harm from drug interactions. has the following advice for consumers:

  • Be aware that foods and dietary supplements can interact with medicines. Carefully read product labels, and ask your pharmacist for advice.
  • Check the labels on the containers of your prescription medicines, as provided by your pharmacy. These labels can remind you of potential drug-food interactions.
  • Be sure you know what fluids you can take with your medicine. Milk, fruit juices, or food can affect the absorption and action of some medicines. Most medicines are best taken with plain water, but there are some exceptions. Your pharmacist can provide advice to help you take all of your medicines properly.
  • When you pick up your prescriptions from your pharmacy, listen to what the pharmacist tells you about your medicines. Ask the pharmacist whether any of the medicines you are taking might interact with other medicines or with food.
  • Use the same pharmacy to fill all your prescriptions. Be sure to tell your pharmacist about any nonprescription medicines that you take, including natural products and food supplements. This information will allow your pharmacist to check for all potential drug interactions.
  • Keep a list of all your medicines and the instructions on how you take them. Be sure to include all of your medicines, as well as natural products and food supplements, on your list. Always show the list to healthcare providers whenever you receive care.
  • When selecting non-prescription medicines, including natural or herbal medicines, carefully read the information on the label. Ask your pharmacist for assistance with selecting these products. Be sure to discuss the other medicines you are taking, and ask whether the new product might interact with them.

Read more about preventing harm from drug interactions.

Read more about keeping a list of your medicines.

Tips for practitioners:

  • Ask to see each patient's current list of medicines and nutritional supplements before prescribing, dispensing, or administering any medicine.
  • Ensure that drug interaction screening is completed before any medicine is dispensed or administered.
  • When appropriate, inquire about your patient's dietary habits to rule out the possibility of a drug-food interaction. Initiate a conversation about drug-drug and drug-food interactions and how to avoid them.
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