Common Side Effects

• The most common side effect that users of codeine frequently experience is nausea. Nausea is seen as a minor side effect of the body, since it tends to rapidly subside. Other common side effects of codeine are flushing, feeling lightheaded, dizziness, dry mouth, constipation, sweating and drowsiness. If these side effects do not go away quickly, or if they get worse, you should notify your doctor.
  
  

Uncommon and Serious Side Effects

• Uncommon and possibly serious side effects with codeine use are mood or mental changes, such as confusion, disorientation, restlessness and agitation; shallow or slow breathing; irregular, slow, or rapid heartbeat; changes in vision; and passing out. If you have any of these side effects, you should seek medical help immediately.
  
  

Rare and Severe Side Effects

• Some other extremely rare codeine side effects are also extremely serious. These side effects call for emergency medical assistance as soon as possible. They are changes in the amount of urine produced and severe abdominal pain.
  
  

Allergic Reactions

• Although severe allergic reactions to this medication are uncommon, they are possible, and require emergency medical attention. Some signs of allergic reaction to codeine include extreme dizziness, having problems breathing, swelling, skin rash, hives and itchiness.
  
  

Elderly Individuals

• Elderly persons planning on taking codeine to reduce pain should be particularly careful, as they are more prone to experiencing the medicine's negative side effects, particularly the problems with urinating, shallow or slow breathing, and drowsiness.