What are side effects of medicines?

Side effects are unwanted effects of taking a medicine. They are also known as adverse reactions.

Not all side effects are serious, but some are. Some examples of side effects are:

• dry mouth
• rash
• nausea
• upset stomach
• bloating or constipation
• headache
• drowsiness

Vaccines can have side effects too. The most likely side effect of a vaccine is soreness at the injection site.

When you start a new medicine ask your pharmacist about any side effects.

What is an adverse event?

An adverse event is something that results in, or could have resulted, in harm to a person. A medicine side effect is a type of adverse event.

Adverse events can also happen when you use a medical device such as a pacemaker or joint replacement.

An adverse event does not necessarily mean that there is something wrong with the medicine, device or vaccine.

What types of medicines can cause side effects?

All types of medicines can have side effects. This includes:

• prescription medicines
• over-the-counter medicines that you can buy from a pharmacy, supermarket or other shops
• vaccines
• vitamins and minerals
• herbal, complementary, alternative and natural medicines

Even though all medicines can cause side effects, not everyone will get them.

When do side effects happen?

You can get a side effect from a medicine straight away or later.

Sometimes side effects of medicines get better over time. For example, a new medicine might make you feel nauseous at first but this will go away after you take the medicine for a while.

Sometimes side effects don't happen right away. They can develop after you have been taking the medicine for a while.

Side effects can also occur due to interactions with:

• prescription medicines
• over-the-counter medicines
• supplements
• food
• alcohol

Can medicine side effects be prevented?

Not all side effects can be prevented, but there are some things you can do to make them less likely.

Always take your medicine according to the instructions.

Specific instructions you might be given for a medicine include:

• starting with a low dose and increasing that dose slowly over time
• taking your medicine with meals
• taking your medicine on an empty stomach (before you eat)
• taking your medicine at a specific time of the day
• staying out of the sun
• avoiding alcohol

If you don't understand the instructions, check with your pharmacist.

If you are having trouble with side effects of a medicine, talk to your doctor. There may be things you can do to reduce the side effects or other medicines that suit you better.

Never take a medicine that was prescribed for someone else.

Vaccinations and side effects

Like other medicines, vaccines can have side effects. However, vaccines generally offer benefits that greatly outweigh their risks.

The Australian Government monitors the safety of vaccines through surveillance programs.

For example, each year in Australia influenza (flu) causes around 3,000 deaths in people older than 50 years of age. The main side effect of the influenza vaccine is swelling, redness or pain at the injection site, or fever in children. Serious adverse events such as Guillain-Barré syndrome are very rare.

Passive and active surveillance

Passive surveillance is when you decide to report side effects to your:

• doctor
• pharmacist
• the Therapeutic Goods Administration (TGA)

Find out more about how to report a problem with a medicine.

Active surveillance is when you are asked about any side effects after having a vaccine. In Australia this is done using a system called AusVaxSafety which sends you a short text message.

The SMS asks if you have had a reaction to the vaccine. Experts look at the SMS responses to make sure that any safety issues are found quickly.

Where can I get information about side effects?

Your doctor and pharmacist are the best people to speak to about potential side effects.

Here are some questions you might want to ask them:

• What are the possible side effects of this medicine?
• Does this medicine have any serious side effects?
• How often do these side effects happen?
• What can I do to avoid or lower my risk of side effects?
• Do the side effects get better with time?
• What should I do if I think I'm having a side effect?

The Consumer Medicine Information (CMI)

You can also get information on side effects from the medicine's Consumer Medicine Information (CMI) leaflet.

All prescription medicines and some non-prescription medicines have a CMI. You can search for CMIs in healthdirect's medicines section or at the medicines.org.au website.

Your pharmacist should offer you the CMI when you are prescribed a new medicine. You can also ask your pharmacist or doctor for a copy of the CMI.

Resources and Support

If it's not an emergency but side effects are bothering you, talk to your doctor or pharmacist.

If you think you have taken too much medicine, call the Poisons Information Centre, 24 hours a day on 13 11 26.

Find out how to report medicine problems or side effects to the TGA.

You can also call healthdirect on 1800 022 222 (known as NURSE-ON-CALL in Victoria) to speak to a registered nurse if you think you are having a side effect to a medicine or vaccine.

Other languages

If you require information in languages other than English, NPS MedicineWise has several translated factsheets on medicines and side effects.