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

Side effects of antibiotics that affect the digestive system include: 

• being sick
• feeling sick
• 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 one person in 15 has 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 a medication known as antihistamines.

However, if you are concerned or your symptoms fail to respond to treatment then you should call your GP for advice. If you can't contact your GP, call NHS 111.

In rare cases (estimated to be somewhere between one and five in 10,000) 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 breathing difficulties due to 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
• unconsciousness

Anaphylaxis is a medical emergency and, without prompt treatment, can be life-threatening. Dial 999 immediately and ask for an ambulance if you think that you or someone you know is experiencing anaphylaxis.