• All medicines can cause unwanted side effects. Medicines include prescription, over-the-counter and complementary medicines (herbal preparations and vitamins).
  • If you are worried about any of your medicines, seek immediate medical attention.
  • Active ingredients in medicines can ‘clash’. So, taking more than one medicine at the same time can increase the risk of side effects. 
  • Tell your doctor about all the medicines you are taking. You may like to have an annual review of all your medications.

A side effect is an unwanted symptom caused by medical treatment. All medicines can cause side effects, including prescription, over-the-counter and complementary medicines. Complementary medicines include herbal preparations, vitamins, and some products dispensed by naturopaths and other practitioners of complementary medicine. 

Around 230,000 Australians are admitted to hospital every year because of problems with their medicines, including side effects. While most side effects can be managed, some can be very serious and may even cause death.  

It is in your best interests to manage your medicines wisely. See your doctor or pharmacist for further information and advice.

Prescription medicines can cause side effects

All medicines can cause unwanted side effects. For example, some antibiotics can cause allergic reactions in around five per cent of the population. Skin rashes are a common reaction. But, it is not always easy to tell if the reaction is caused by the medicine or the illness.

Interactions between other medicines the person may be taking is a further complication. Interactions can happen between prescription, over-the-counter and complementary medicines. 

Complementary medicines also cause side effects 

About 60 per cent of Australians use complementary medicines at least once a year. Many people believe that they are safer because they come from natural sources. This isn’t always true.

Some herbal remedies act on the body as powerfully as any conventional medicine, and unwanted side effects can occur.

Some examples of complementary medicines that can cause side effects include: 

  • echinacea – more than 20 different types of reactions have been reported. Some include asthma attacks, hives, swelling, aching muscles and gastrointestinal upsets
  • feverfew – pregnant women should not use this herb, as it can trigger uterine contractions. In animal experiments, feverfew triggered spontaneous abortions (miscarriages)

Complementary medicines can interact with prescription medicines

About one in five Australians take both complementary and prescription medicines. Active ingredients in these medicines can interact, increasing the risk of side effects.

Some medicines have similar active ingredients, that may act in the same way. Other complementary medicines may make the prescription medicine more or less effective.

Some combinations that can put people’s health at risk include: 

  • Echinacea may interact with medications broken down by the liver. 
  • Many complementary medicines (including feverfew, ginkgo and chamomile) may increase the risk of bleeding in people taking anticoagulant medicines (such as warfarin) and anti-inflammatory medicines (such as aspirin).
  • St John’s wort increases serotonin. If taken with other medicines that increase serotonin (such as antidepressants) it can cause serotonin toxicity. Serotonin toxicity can range from mild to life threatening. Symptoms include tremors, high temperature and low blood pressure. 

For advice about complementary medicines, speak with your doctor or other health professional. 

Alcohol used with medicines can cause side effects

Drinking alcohol with some medicines can also cause unwanted (and sometimes dangerous) side effects. For example:

  • Alcohol can cause drowsiness or dizziness when taken with (some) antihistamines, antidepressants, sleeping tablets or medicines for anxiety.
  • Alcohol can affect medicines for high blood pressure and travel sickness, and some pain medicines can also be affected by alcohol.
  • Some antibiotics interact negatively with alcohol and some can cause a severe reaction. Symptoms can include upset stomach, skin flushing, headache, a fast or irregular heartbeat, drowsiness or dizziness.

Remember that alcohol can stay in your system for several hours after your last drink, so it is important to be aware that interactions can occur long after you stop drinking.
Talk to your doctor or other health professional for advice about your medication and drinking alcohol.

What to do if you experience side effects

If you experience side effects when taking medication:

  • In an emergency, call triple zero (000).
  • Note the side effects and consult your doctor or pharmacist if you have any concerns. They may need to adjust the dose or type of medicine you use.
  • Call the NPS Medicines Line on 1300 633 424 or the Adverse Medicines Events Line on 1300 134 237 for advice. These phone-line services allow consumers to report or receive advice on side effects. They are not emergency services.

How to reduce the risk of side effects

To reduce your risk of experiencing side-effects:

  • Take all medicines as prescribed by your doctor.
  • Don’t take anyone else’s medicines.
  • Learn about your medication. All prescription medicines have an information leaflet called Consumer Medicine Information (CMI). This gives detailed information on the medicine in plain English, including how to use it, side effects and precautions. Your pharmacist can also give you the CMI for your medicine.
  • Speak to your pharmacist if you buy over-the-counter or complementary medicines. They can advise you about side effects and interactions with other medicines you are taking. Be aware that medicines you buy in the supermarket can also cause side effects.
  • Tell your doctor about all the medicines you take, including prescription, over-the-counter and complementary medicines. 
  • Have an annual review of all the medicines you take. This is important for older people as they are more likely to experience side effects. A review can take place in a pharmacy or at home. Ask your doctor for more information about medication reviews. 

Other things you can do to reduce your risk of side effects from medicines include:

  • Ask your doctor if improving your lifestyle could reduce your need for medication. Some conditions can be better managed with changes to your diet and regular exercise.
  • Return unwanted and out-of-date medicines to your pharmacy for safe disposal. This is a free service.
  • Talk to your pharmacist about dosage aids that can help you organise your pill taking. You may be at risk of making mistakes if you take many different medicines at different times.
  • Ask your doctor or pharmacist questions so you understand the benefits and risks of your medicines.

Where to get help


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This page has been produced in consultation with and approved by: NPS MEDICINEWISE

Last updated: April 2019

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