decongestants tend to unblock your nose and chest, it depends or how clogged you feel. An antihistamine is supposed to block or slow the release of histamine, which produces the excess mucus. If your nose is running and you are sneezing, you may can get by with just an antihistamine. Now if you are like me and woke up sneezing your head off, but your lungs and nasal passages are still clogged, you need to take the decongestant too.