Cardiovascular Effects

• A possible side effect of this medication is chest pain. It may also cause abnormal heart rhythms; your heart may feel as if it is skipping around. If you have been diagnosed with any kind of heart disease, your doctor may refrain from prescribing this for you.
  
  

Central Nervous System Effects

• Dizziness may occur while taking this medication, especially when you stand up. It may cause a headache as well. Fatigue could be an issue because you may not be able to sleep well at night.
  
  

Gastrointestinal Effects

• An upset stomach and vomiting may occur, and diarrhea is not uncommon. Pain may occur in your abdomen. Since this medicine can become toxic to your liver, you may notice a yellow color to your skin and the whites of your eyes; this is called jaundice, and it should be reported immediately to your doctor, or you should get to an emergency room as soon as possible. If you have been diagnosed with any form of liver disease, tell your doctor before you take this medication. Your stools could be the color of clay. A low-grade fever and acid reflux are possible as well.
  A more serious side effect is pseudomembranous colitis, otherwise known as C-diff. This is a condition in which all of the good bacteria in your intestines is overrun by the bad bacteria, resulting in severe, watery diarrhea. This must be treated immediately, as it is contagious and could cause further problems.
  
  

Genitourinary Effects

• This medication can cause women to develop a yeast infection, as well as vaginal itching. Women may also have discharge from their vagina that is foul-smelling and white in color.
  It is also a possibility that a kidney infection or inflammation could develop. If you have had kidney disease, notify your doctor of this before taking Z-pak.
  
  

Other Effects

• It is possible that you could develop a rash on your skin. It may also cause tinnitus, which is a ringing sound in your ears, or problems tasting or smelling. Swelling is yet another possibility, especially if you are allergic to this medication.
  It's also important to let your doctor know if you are pregnant or breastfeeding, since this medication could cause problems with your baby's health; however, it can be given to you for a more serious infection that could become deadly.