Diphenhydramine may cause drowsiness, dizziness, gastrointestinal disturbance; dry mouth nose and throat; difficulty in urination or blurred vision. Less frequently it may cause palpitations, tremor, convulsions or paraesthesia. Hypersensitivity reactions have been reported, in particular, skin rashes, erythema, urticaria and angiodema. Gastro-intestinal discomfort, nausea and vomiting have occasionally been reported with guaifenesin particularly in large doses. Adverse reactions to levomenthol at the low concentration present are not anticipated.