If you experience any of these symptoms, check with your doctor immediately. On rare occasions some types of penicillin may cause severe abdominal or stomach cramps, pain, or bloating or severe or bloody diarrhea.

If diarrhea is severe and watery, or if it has blood in it, check with your doctor immediately.

Other rare side effects include fever, increased thirst, severe nausea or vomiting, unusual tiredness or weakness, weight loss, seizures, or unusual bleeding or bruising.

If any of these occur (and they may not occur until several weeks after you stop taking the medicine), check with your doctor immediately.

Common, less serious, side effects that some people experience include mild diarrhea and mild nausea or vomiting.

Diarrhea medicine containing kaolin (such as Kaopectate or Donnagel) or attapulgite (such as Diasorb) may be taken to relieve mild diarrhea.

However, some ingredients in diarrhea medicine, such as lactose, may make diarrhea worse, so read labels carefully. Occasionally, certain types of penicillin may cause the tongue to darken or discolor.

This condition will probably be temporary and will go away when the medicine is stopped.

Before Taking This Medicine

If you have ever had an allergic reaction to penicillin, be sure to let your doctor know, preferably at your first visit, even if you do not then have an infection.