Is it safe to take mucinex (dextromethorphan, guaifenesin, phenylephrine) with 40 mg celexa?

Better not,: the dextromethorphan component of the Mucinex combo would interact with celexa, plain Mucinex, just guaifenesin, is a better alternative. Good that you asked, always exercise caution with multiple medications, best wishes

No: Guaifenisin when mixed with Celexa can cause seritonin syndrome. Besides, it is of very little use for a cold anyhow. See these links about both statements: http://www.cochrane.org/CD001831/ARI_over-the-counter-otc-medications-for-acute-cough-in-children-and-adults-in-community-settings http://toxicology.ucsd.edu/art%203%20serotonin%20syndrome.pdf