The most common side effects of antibiotics affect the digestive system. These occur in around 1 in 10 people.

Side effects of antibiotics that affect the digestive system include: 

  • vomiting
  • nausea (feeling like you may vomit) 
  • diarrhoea 
  • bloating and indigestion
  • abdominal pain
  • loss of appetite

These side effects are usually mild and should pass once you finish your course of treatment.

If you experience any additional side effects other than those listed above, you should contact your GP or the doctor in charge of your care for advice.

Antibiotic allergic reactions

Around 1 in 15 people have an allergic reaction to antibiotics, especially penicillin and cephalosporins. In most cases, the allergic reaction is mild to moderate and can take the form of:

  • a raised, itchy skin rash (urticaria, or hives)
  • coughing 
  • wheezing
  • tightness of the throat, which can cause breathing difficulties

These mild to moderate allergic reactions can usually be successfully treated by taking antihistamines.

But if you're concerned, or your symptoms don't respond to treatment, you should call your GP for advice. If you can't contact your GP, call NHS 111.

In rare cases, an antibiotic can cause a severe and potentially life-threatening allergic reaction known as anaphylaxis.

Initial symptoms of anaphylaxis are often the same as above and can lead to:

  • a rapid heartbeat 
  • increasing difficulty breathing caused by swelling and tightening of the neck
  • a sudden intense feeling of apprehension and fear
  • a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused
  • falling unconsciousness

Anaphylaxis is a medical emergency and can be life-threatening if prompt treatment isn't given. Dial 999 immediately and ask for an ambulance if you think you or someone around you is experiencing anaphylaxis.

Tetracyclines and sensitivity to light 

Tetracyclines can make your skin sensitive to sunlight and artificial sources of light, such as sun lamps and sunbeds.

You should avoid prolonged exposure to bright light while taking these drugs.

Reporting side effects

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine you are taking.

It's run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA).

Page last reviewed: 09/06/2016

Next review due: 01/12/2018