Understanding drug interactions

by | Sep 13, 2022 | Medicine

It’s important for anyone who is taking a medicine to be aware of possible drug interactions. This is because drug interactions can change how well your medicine works or even lead to unexpected side effects. So what can you do to protect yourself against drug interactions?

What are drug interactions and when do they occur?

Drug interactions occur when another medicine (including herbal supplements), food or drink (including alcohol) changes how a medicine you are taking works or changes its side effects.

There are many different types of drug interactions, but the most common are:¹

  • taking two or more medicines with similar effects on the body, so that the combined effect is much stronger than you need.
  • taking a medicine that makes your body absorb or excrete another medicine you are taking slower or faster than usual, so that your usual dose is either too strong or not strong enough.

Examples of common drug interactions


Statins are a type of medicine used to lower cholesterol. If taken at the same time as grapefruit juice, the levels of some statins in the blood can rise. This is because grapefruit juice can lower the levels of enzymes in your liver responsible for breaking down statins. As a result, there is an increased risk of side effects such as muscle pain or even severe muscle injury (known as rhabdomyolysis).²

 Selective serotonin reuptake inhibitors or SSRIs

Selective serotonin reuptake inhibitors or SSRIs are a type of antidepressant that work by increasing levels of the ‘feel good hormone’ serotonin in the brain. If SSRIs are taken with other medications that also release serotonin, such as the herb St. John’s wort, this can result in excessive levels of serotonin in the body. This serious drug reaction is called serotonin syndrome. SSRIs can also interact with other medicines such as antiplatelets to increase the risk of bleeding.³

 Non-steroidal anti-inflammatory drugs or NSAIDs

Non-steroidal anti-inflammatory drugs or NSAIDs are commonly used to relieve pain, reduce inflammation and to treat a fever.4 If NSAIDs are taken with certain other medicines, this can affect how well either medicine works and increase the risk of side effects. These medicines includes other NSAIDs, low-dose aspirin or warfarin (used to prevent blood clots), diuretics (sometimes used to treat high blood pressure) and SSRIs (a type of antidepressant).⁴

What to double check before you take a new medicine

Communication with your doctor is crucial to help prevent drug interactions. If you take several different prescription medicines, see more than one doctor, or have certain health conditions, make sure your doctor is aware of all the medicines you take before you order your scripts online. 

It is also important to ask your doctor about possible interactions with any over-the-counter drugs, dietary supplements, or vitamins and minerals that you may be taking, as well as the foods that you eat. 

Remember drug interactions are usually preventable if you take a proactive approach! 

If you have any questions about drug interactions, please speak to your doctor or ask our Pharmacist a question.

References: 1. NPS MedicineWise. Understanding drug interactions. Available at: https://www.nps.org.au/consumers/understanding-drug-interactions#. Accessed August 2022. 2. NHS. Considerations: statins. Available at: https://www.nhs.uk/conditions/statins/considerations. Accessed August 2022. 3. NHS. Cautions – Selective serotonin reuptake inhibitors (SSRIs). Available at: https://www.nhs.uk/mental-health/talking-therapies-medicine-treatments/medicines-and-psychiatry/ssri-antidepressants/considerations Accessed August 2022. 3. NHS. NSAIDs. Available at: https://www.nhs.uk/conditions/nsaids. Accessed August 2022.


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Medically reviewed by Dr Matt Cullen

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