Are there any side effects of mucinex (guaifenesin)?

Mucinex (guaifenesin) side effects. Like any medication, there are side effects that can occur with the use of mucinex (guaifenesin). Side effect do not always occur in everyone that takes a medication. Most common with Mucinex (guaifenesin) is nausea and vomiting. Can be as serious as facial swelling: lips, tongue. Always check with your prescribing doctor and pharmacist.