Antibiotics - Side effects 

Side effects of antibiotics  

Tetracyclines and sensitivity to light 

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

You should avoid prolonged exposure to bright light while taking tetracyclines.

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.


Page last reviewed: 05/06/2014

Next review due: 05/06/2016

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The 2 comments posted are personal views. Any information they give has not been checked and may not be accurate.

douzpwa said on 02 September 2014

Been allergic to penicillin over 30 years! I too would like to know how long it takes for the allergy to go out system i still have red patches on my stomach and feel sick! Puff pant going upstairs though i have been going to gym using bike and cross trainer for couple hours a day! i had severe reaction like Trisha44 after my GP wrongly gave me penicillin, i took 1 day dose 3 pills woke up about 20-30 times thinking i had long sleeps yet it was only about within 2hrs. I woke up could not stop shaking, felt dizzy and sick chittery, within 24hrs i could see my skin looking like start of porridge before breaking out red fading and reappearing red coloured nippy and itchy head to toe my skin going red all over was like a lobster inside my mouth on bottom of my tongue did not feel right like it was swelling or numb like and i was very exhausted.

Been off work since 1st July start back 12th Sept though i still as said have patches of red around stomach and feel sickish at times and diarohea too! I did spend a week in hospital and they said they had never seen such a reaction to penicillin, whilst in hospital one day it looked like i was coming out in blisters before very eyes i could feel under my skin was developing like lumpy lumps. A&E Doc came to ward took mobile pics sent them to dermotologist who had to come in about 2am to check me herself.

I thought i was a gonna got very scared even texted my mate left a msg for him to pass on to my family. Thankfully after checking me out Dermo thought the allergy was peaking and by next day i was back to being red like a lobster and got out once my temp and blood was ok! Spent 7 days in! Took long time to recover even after all these weeks i still dont feel right but need to go back to work !

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trish44 said on 12 August 2014

would love to know how long these take to get out of your system as had a severe reaction which has left me tire and no in energy

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Reporting side effects

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

It is run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA). See the Yellow Card Scheme website for more information.

The Yellow Card Scheme

The MHRA has produced a video that explains how the Yellow Card Scheme can be used to report the side effects of medication