Can you take NyQuil with benzonatate?

NyQuil already contains doxylamine, which is almost exactly like Benadryl (diphenhydramine), so it wouldn't be a good idea to take them together since that would be a "duplication of therapy". If the NyQuil isn't keeping your congestion down, you could probably take 25 mg of Benadryl (diphenhydramine) and be OK.