Alcon Plus Syrup is used to treat symptoms of the common cold and allergies like sneezing, runny/stuffy nose, fever, headache, body pains, congestion, or watery eyes. It works by blocking the action of histamine, a substance responsible for causing allergic reactions. It also shrinks the blood vessels in the nasal passage. Thus, it provides relief from congestion and decreases excess mucus production. Some people may experience drowsiness, nervousness, headache, dizziness, insomnia (difficulty in falling or staying asleep), blurred vision, constipation and dry mouth. Before taking this medicine, you should tell your doctor if you are allergic to any of its components or if you are pregnant/breastfeeding, and about all the medications you are taking and pre-existing medical conditions.