Would a prescription antihistamine interact with 20mg celexa (citalopram)?

Usually not. Most are ok to take and no interaction but depends on which med.
Unlikely. Celexa (citalopram) can interact with a number of medications, both prescription and over the counter, but antihistamines are not known to interact. You should avoid decongestants, "nsaids" - aspirin, ibuprofen, naproxen, etc., cough medicines with dm (dextromethorphan), narcotics, and many street drugs.

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