Helping the Medicine Go Down: Drug Interactions You Need to Know About

Man dispensing medication into his hand from pill bottle.


The percentage of Canadians aged 45 to 64 taking medications is 55 per cent, while those 65 to 79 is 83 per cent. And people 75 and older take an average of six medications a day. Many of these are needed but can have side effects, however, and the more medications, the more potential for problems.

Adverse drug reactions (ADRs) are one of the leading causes of morbidity and mortality in health care and one of the top reasons for ER visits. 

Here, some medication interactions you should know about.

  • Medications at especially high risk for interactions with other medications, food and herbs: anticonvulsants, antibiotics and anticoagulants (blood thinners). Specifically, fluoroquinolone antibiotics (e.g., Cipro) are less effective if taken with aluminum (antacids), magnesium (Maalox), calcium or iron.
  • Calcium can decrease effectiveness of tetracycline antibiotics. Calcium also decreases thyroid medication absorption so take them four or more hours apart.
  • Grapefruit juice can inhibit metabolism and thereby increase drug levels of amiodarone, Lipitor and Viagra.
  • Vitamin K (herbs, dark leafy greens, brussels sprouts, broccoli, asparagus and cabbage) makes Coumadin less effective.
  • Warfarin (Coumadin) interacts with many other medications; some increase its effect, others decrease it.      

The Canadian Patient Safety Institute (CPSI) advises you to review your medications with a doctor, nurse or pharmacist if you are:

  • Over the age of 65
  • Taking five or more medications
  •  Recently discharged from hospital
  •  Concerned about side effects

The CPSI recommends that you:

1. KNOW all your medications – prescription, over-the-counter, and naturopathic. Take the list with you to all medical appointments.

2. CHECK with your pharmacist, doctor or nurse to confirm you are taking all medications properly.

3. ASK to review all of your meds when your doctor starts, stops or changes any of your prescriptions.

4. REVIEW your medications with your pharmacist when filling or refilling a prescription and when changing any non-prescription medication or supplement.

5. CONSULT your doctor or health-care professional before stopping or changing any medication.

Sometimes medications are absolutely essential and life-saving. But the more medications you take, the more potential for side effects and interactions with each other and with other substances.