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Revised: 22 May 2019

Safety Information

Adverse Reactions to Medicines

What is an adverse reaction?
What is meant by a common or rare adverse reaction?
How can I reduce the risk of adverse reactions?
Do adverse reactions always come on straight away?
Can I report an adverse reaction?
What suspected adverse reacions have been reported to CARM for my medicine(s)?

What is an adverse reaction?

An adverse drug reaction is an unexpected or unintended effect suspected to be caused by a medicine.

All medicines can cause adverse reactions in some people. Adverse reactions can range from headaches and upset stomach to more serious reactions such as liver or kidney injury. Some adverse reactions can be predicted, but some adverse reactions occur unexpectedly once many people take the medicine (eg, severe allergy). Most people take medicines without suffering any serious adverse reactions.

The best way to know what the possible adverse reactions might be is to read the medicine data sheet and/or consumer medicine information available on the Medsafe website.

Find a medicine data sheet or consumer medicine information

What is meant by a common or rare adverse reaction?

The chance of having an adverse reaction can be described as:

  • very common – this means that 1 in every 10 people taking the medicine are likely to have the adverse reaction
  • common – this means that between 1 in 10 and 1 in 100 people may be affected
  • uncommon – this means that between 1 in 100 and 1 in 1,000 people may be affected
  • rare – means that between 1 in 1,000 and 1 in 10,000 people may be affected
  • very rare – means that fewer than 1 in 10,000 people may be affected.

If an adverse reaction affects 1 person in every 10,000 people taking it, then 9,999 people out of 10,000 are not expected to have that adverse reaction.

How can I reduce the risk of adverse reactions?

  • Always take medicines as advised by a pharmacist, doctor or prescriber (eg, some medicines that can cause drowsiness are best taken at night).
  • If the medicine is bought always follow the directions on the package.
  • Never take medicines prescribed for other people.
  • Never take more medicine than recommended.
  • Be careful about mixing medicines. Some medicines, including complementary medicines and medicines bought in a pharmacy or supermarket should not be taken together. Patients taking prescription medicines should discuss with their pharmacist or doctor whether any medicines available over-the-counter should be avoided.
  • Be careful about taking medicines with alcohol or certain foods.
  • Patients should always tell their doctor if they are taking medicines bought in a pharmacy, supermarket (including complementary medicines and food supplements).

Do adverse reactions always come on straight away?

It depends on the medicine and the person.

In general, adverse reactions are most likely to happen soon after medicines are started or after increasing the dose. Other adverse reactions can occur after long term use. A patient's doctor can monitor for these reactions to prevent them occurring (eg, blood tests with warfarin).

Some adverse reactions will go away if the medicine is continued. However, any concerns should be discussed with a doctor or pharmacist.

You should not make any changes to your medicine or stop taking your medicine without first talking to your doctor or a pharmacist.

Can I report an adverse reaction?

Anyone living in New Zealand who thinks they may have experienced an adverse reaction due to a medicine can report this to the Centre for Adverse Reactions Monitoring (CARM). You do not need to be a healthcare professional to report an adverse reaction.

CARM informs Medsafe of any medicine related safety issues detected.

How can I report an adverse reaction to a medicine?

What suspected adverse reactions have been reported to CARM for my medicine(s)?

You can find information on reports of suspected adverse reactions to medicines reported to Centre for Adverse Reactions Monitoring (CARM) using the Suspected Medicine Adverse Reaction Search (SMARS).

Medsafe publishes communications about safety concerns to help consumers and healthcare professionals make informed decisions about their use of a medicine.

Search for reports of suspected adverse reactions to medicines (SMARS)

Find out more about Medsafe's safety communications

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