The side effects of cough syrup can vary, but the most common ones are drowsiness and dizziness, as noted on WebMd. There are many different brands and types of cough syrup, resulting is differing effects.
Some cough syrups may have more noticeable side effects, according to WebMD. Nausea and vomiting are possible in some cases. Allergic reactions are possible but rare. Symptoms of an allergic reaction to cough syrup include rash, itching, swelling, severe dizziness and trouble breathing.
Many cough syrup products contain an expectorant known as guaifenesin. WebMD states that expectorants work by thinning and loosening mucus in the airways. Some cough syrups also contain cough suppressants such as dextromethorphan, which actually works on the part of the brain that controls the impulse to cough. This combination of medicines suppresses coughing to limit the risk of irritation to the throat, while the expectorant helps to remove the mucus that is causing the impulse to cough.
WebMD also claims that many cough syrups contain sugar or alcohol to improve the taste of the syrup. For this reason, those with diabetes or liver disease should consult a doctor before self-medicating with cough syrup. For similar reasons, pregnant women shoulc consult a doctor before using cough syrup.