HIV in Canada: A primer for service providers


Drug Interactions

Key Points

  • Prescription drugs, non-prescription (over-the-counter) drugs, street drugs, herbal products and supplements can potentially cause drug interactions.
  • It is important that healthcare providers know about all the drugs or products a patient is taking to help avoid drug interactions.

The types of prescription or non-prescription (over-the-counter) drugs that are likely to cause interactions with antiretroviral therapy (ART) include certain antifungal drugs and antibiotics, acid-reducing agents and some anti-seizure drugs. Other drugs that may cause interactions include drugs used to treat depression, antihistamines, drugs to control heart rhythm, painkillers derived from opium, sedatives, drugs to thin the blood, drugs used to treat opiate addiction (such as methadone and buprenorphine), drugs to treat erectile dysfunction (such as Viagra, Cialis and Levitra) and some drugs used to treat tuberculosis, especially rifampin. Also, some HIV drugs can affect the effectiveness of other medications, such as the birth control pill; this drug interaction could result in unwanted pregnancies.

Use of street drugs may also cause interactions with HIV drugs. There are few studies of these types of interactions, but there have been reports of overdoses and deaths when people have taken street drugs and ART.

There has been very little research on interactions between herbal products and HIV drugs. Treatment guidelines indicate that St. John’s wort should not be taken with any protease inhibitor or non-nucleoside reverse transcriptase inhibitor. The impact of this herb on other drug classes is not known, so the use of St. John’s wort when taking ART is best avoided. Other herbs, such as milk thistle, may also interact with HIV drugs or other prescription medicines.

Healthcare providers need to know all the drugs – prescription, over-the-counter and street drugs – that people with HIV are using, as well as any herbs and supplements, to advise them about avoiding drug interactions. The routine inclusion by the physician of non-judgemental questions about the use of any other drugs, herbs or supplements in the patient consultation may be a simple method of encouraging such disclosure. Pharmacists also play an important role in avoiding drug interactions.


HIV/HCV Drug Therapy Guide – Toronto General Hospital

HIV drug interactions – University of Liverpool


  1. Furler M, Einarson T, Walmsley S, et al. Use of complementary and alternative medicine by HIV-infected outpatients in Ontario, Canada. AIDS Patient Care and STDs. 2003;17(4):155–168.
  2. AIDS Infonet. Fact sheet 407: Drug Interactions. 2014. Available from:

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