Hydrocodone is not available in parenteral or any other non-oral forms. Adverse effects. Common side effects of hydrocodone are nausea, vomiting, constipation, drowsiness, dizziness, lightheadedness, anxiety, abnormally happy or sad mood, dry throat, difficulty urinating, rash, itching, and narrowing of the pupils. Serious side effects include slowed or irregular breathing and chest tightness.