Final answer:
The nurse should reassure the patient that mild nausea is a common side effect of guaifenesin and implement comfort measures, as it is not a severe adverse effect.
Step-by-step explanation:
If a patient taking guaifenesin reports mild nausea but exhibits stable vital signs and an unremarkable gastrointestinal assessment, the appropriate nursing action would be D- Reassure the patient that nausea is a common adverse effect of this drug, and implement comfort measures. The nurse should educate the patient that while guaifenesin is often well-tolerated, gastrointestinal symptoms like nausea can occur. However, these are not typically severe and can usually be managed with simple interventions such as taking the medication with food, ensuring adequate hydration, or using over-the-counter remedies if approved by their health care provider.