Stomach pain, nausea, vomiting and diarrhea are possible side effects of Tussin cough syrup, according to Drugs.com. Headache, dizziness, skin rash and hives are other possible side effects. Most people tolerate Tussin well, and gastrointestinal side effects are most likely to occur when people exceed recommended dosages.
When taking Tussin cough syrup, using the included measuring device provides the proper dosage, making overdose less likely, advises WebMD. This formula may include sugar or alcohol, which may be problematic for people with diabetes or liver disease. While serious side effects rarely occur, individuals who experience itching or swelling, especially of the face, throat or tongue; rash; extreme dizziness; or breathing difficulties should seek immediate medical attention. No proof exists that cough and cold medications are safe or effective for use by children under the age of 6, so young children should not take Tussin cough syrup unless a physician directs them to do so.
Guaifenesin is the active ingredient in Tussin, explains Drugs.com. It is an expectorant that thins and loosens mucus, eases breathing and clears congestion, states WebMD. It treats coughs and congestion due to upper respiratory issues, such as bronchitis and the common cold, but is normally not effective for coughs due to smoking, emphysema and chronic bronchitis. Although guaifenesin eases coughing and congestion, it does not cure the common cold or shorten its duration.