Delcon Tablet (chlorpheniramine maleate and phenylephrine) is used for cold and allergy symptoms. Like all medicines, it may cause some side effects, although not everyone gets them. Common side effects include drowsiness, dizziness, headache, dry mouth, dry nose or throat, constipation, and mild stomach upset. In some cases, it may cause trouble sleeping or restlessness. Because it can make you drowsy, you should avoid driving or using heavy machinery until you know how it affects you. Drinking enough water and resting can help reduce mild side effects. If any side effects become severe or persistent, or if you notice unusual symptoms, you should stop the medicine and consult your doctor immediately.