Hi Carol, according to an article I read from the Mayo Clinic, Doxycycline is not listed as a sulfa drug, so you should be okay to take it as prescribed. I also cross referenced the Wikipedia page on Sulfonamides, and it too did not list Doxycycline. If you have other allergies or sensitivities, I'd just double check the inactive ingredients as well to ensure that there is nothing else in there that could disagree with you. If you can refer to the National Drug Code (NDC) printed on your prescription label it should be pretty easy to find the list of inactive ingredients. I hope this helps and feel free to write back!