Side effects of medicines - FAQ

Every medicine has some side effects or risks associated with their use. Although most people take medicines without experiencing any side effects, some may be affected. The following questions and answers should cover some of the questions you may have about medicines and side effects:

Different pills1. What do medicines do?
2. Will my medicine cause side effects?
3. What is meant by a ‘common’ or ‘rare’ side effect?
4. How much medicine should I take?
5. How can I reduce the risk of side effects?
6. Do side effects always come on straight away?
7. What should I do if I feel unwell after taking my medicine?
8. Will my medicine affect my lifestyle?


1. What do medicines do?
The medicine you are taking may:
  • treat your condition - eg an antibiotic, to treat certain infections
  • control your condition - eg a medicine to lower your blood pressure
  • treat the symptoms of your condition - eg a painkiller for toothache
  • prevent you from becoming unwell - eg a vaccination against disease.

2. Will my medicine cause side effects?
The benefit of taking your medicine is expected to be greater than the risk of suffering any unwanted side effects.

Most people take medicines without suffering any unwanted side effects, however all medicines can cause problems. Your patient information leaflet will list all the known side effects linked to your medicine.


3. What is meant by a ‘common’ or ‘rare’ side effect?

The chance (the risk) of having a side effect can be described using words or figures or both. This is how risk may be described in our patient information leaflet:

  • very common means that more than one in ten people taking the medicine are likely to have the side effect
  • common means that between one in ten and one in 100 people are affected
  • uncommon means that between one in 100 and one in 1,000 people are affected
  • rare means that between one in 1,000 and one in 10,000 people are affected
  • very rare means that fewer than one in 10,000people are affected.

Important: if a side effect has a risk of one in 10,000, then 9,999 out of every 10,000 people taking the medicine are not expected to experience that side effect.


4. How much medicine should I take?
To get the most benefit from your medicine you need to take the dose recommended for you, for the length of time advised.

For medicines you have bought without a prescription, the dose is written on the carton or label and in the patient information leaflet. Do not take more than the maximum dose.

For medicines that have been prescribed for you, the dose will be on the pharmacy label.

This dose takes into account your age, weight, how ill you are and any other medicines you may be taking. Only change this dose if you have discussed it with the person who prescribed it.

In general, a high dose of a medicine is more likely to cause side effects. However, high doses may be needed to ensure maximum benefit.

With some medicines, you start on a low dose and gradually increase the dose. With other medicines you will stay on the same dose throughout your course of treatment.

Sometimes, when you need to stop taking a medicine, your doctor will gradually reduce the dose to avoid unpleasant withdrawal effects.

Important: check the patient information leaflet and speak to your doctor or pharmacist if you feel unwell after your dose has changed.


5. How can I reduce the risk of side effects?
Take your medicine as advised by the pharmacist or the person who prescribed it. If you bought the medicine yourself, follow the dosage instructions on the packaging.

Be careful about mixing medicines. Some medicines should not be taken together. Before taking a new medicine, it is important to tell the pharmacist or whoever prescribed it about any other medicines you are already taking. Don’t forget to tell them about herbal remedies or any non-prescription medicines you may have bought in a pharmacy or supermarket.

Be aware that some things can increase the chance of your medicine causing side effects. Your patient information leaflet will tell you about any known risk factors and what you can do to reduce the chance of side effects. For example, you may be able to lower the risk of side effects by not drinking alcohol or not eating certain foods during your course of treatment.


6. Do side effects always come on straight away?
It depends on the medicine and the person. Some side effects can happen immediately - for example an allergic reaction.

Some side effects might not start for several days or weeks - for example skin rashes – or even longer - for example stomach problems with some painkillers.

In general, side effects are most likely to happen soon after you start a new medicine or after your dose has been increased.

Quite often, mild side effects will go away as your body adjusts to the new medicine or dose.


7. What should I do if I feel unwell after taking my medicine?
Check your patient information leaflet for information on side effects and action to take.

If you are worried about a suspected side effect, contact a doctor or pharmacist. You can also get information by calling: NHS 111 Service by dialing '111' (textphone 18001 111) in England, 0845 46 47 (textphone 0845 606 4647) in Wales, or from NHS24 in Scotland on 08454 24 24 24 (textphone 18001 08454 24 24 24).

For worrying or serious effects you may be told to stop taking the medicine, or receive other treatment.

For less serious side effects, you may be advised to continue with your medicine, or change the dose.

You or your healthcare provider can report suspected side effects in confidence to the drug safety watchdog (MHRA) on a Yellow Card.


8. Will my medicine affect my lifestyle?
Although most medicines will not affect your lifestyle, some can. For example:
  • some medicines may affect your vision or coordination or make you sleepy; this may affect your ability to drive, ride a bicycle or perform skilled tasks safely
  • some medicines may affect your sex drive
  • you may need to stop drinking alcohol or eating certain foods while taking some medicines.

Important: your patient information leaflet will tell you about the effects a medicine might have on lifestyle issues and things you should avoid.


Need further advice?
If you need further advice about medicines you can ask your doctor or pharmacist or call NHS Direct & NHS Wales/Galw echyd Cymru on 0845 46 47 (text phone 0845 606 46 47) or NHS 24 (Scotland) on 08454 24 24 24 (textphone 18001 08454 24 24 24).


How do I report a suspected side effect?

Yellow Card forms are available from pharmacies and other outlets across the NHS or from the Yellow Card hotline on freephone 0808 100 3352.

Reports can also be completed on the web at www.mhra.gov.uk/yellowcard  

Taking medicines - some questions and answers about side effectsPDF file (opens in new window) (98Kb)


Page last modified: 29 August 2013