Common side effects of Delsym cough syrup include dizziness, drowsiness and upset stomach, according to Drugs.com. Severe side effects include rashes, hives, difficulty breathing, chest tightness and facial swelling. These rare side effects indicate a potentially life-threatening allergic reaction and necessitate immediate medical attention.
Diabetic patients should consult a doctor prior to taking Delsym, as some varieties affect blood sugar levels, states Drugs.com. Individuals should not take Delsym with alcohol or with certain other medications. Pregnant or breastfeeding mothers and children under 2 years old also should not take this medication. If a cough lasts longer than one week while taking Delsym, it is best to discontinue use and consult a medical professional.