Key takeaways
Doxylamine (Unisom SleepTabs) and guaifenesin/dextromethorphan (Mucinex DM) are both over-the-counter medications, but they are used for different reasons. Doxylamine is an antihistamine used primarily as a sleep aid to treat insomnia, while Mucinex DM is a combination of an expectorant and a cough suppressant used to relieve cough and chest congestion. Doxylamine is taken once daily before bedtime, whereas Mucinex DM can be taken every 4 to 12 hours depending on the formulation. Doxylamine is available as a tablet, while Mucinex DM comes in tablets, liquids, and dissolvable granules. Common side effects of doxylamine include next-day sleepiness and dizziness, while Mucinex DM may cause stomach upset and drowsiness. You should avoid alcohol with both medications, but Mucinex DM also has interactions with certain depression and Parkinson's medications.
