Benadryl Syrup is a medication containing Diphenhydramine Hydrochloride and Ammonium Chloride, and is an expectorant used to increase clearance of mucus. Benadryl Syrup may cause certain adverse reactions such as drowsiness, blurred vision or dry mouth. While some of the above symptoms could be common, some of the stated adverse effects rarely occur. If you experience any side effects (whether or not it is included in the above list), please consult a doctor immediately.