BMJ Group Medical Reference
Doctors don't always give antibiotics for throat infections. But if your symptoms are severe, your doctor may prescribe them. 
Antibiotics are drugs that kill bacteria. They don't work against viruses, which are another cause of tonsillitis. There are lots of different antibiotics. Amoxicillin and erythromycin are two types of antibiotics that doctors use a lot.
Studies of people with a sore throat have found that antibiotics can reduce how long you have symptoms for, but only by about a day. 
Antibiotics can reduce the risk of complications, such as rheumatic fever or an abscess on the tonsils (quinsy).  But these problems are very rare anyway.
You may be given antibiotics if your tonsillitis gets worse over time or if you have a high temperature for a long time.
Antibiotics can have side effects, although these are usually mild. You may get an upset stomach, diarrhoea, or a rash. 
Most doctors are careful not to prescribe antibiotics unless they think you really need them. This is because antibiotics may not work as well in the future if they are used too much. Bacteria can become resistant to antibiotics.
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