Can you take cetirizine and phenylephrine together?

Just to clarify, acetaminophen (paracetamol, APAP) is a painkiller, codeine is an opoid painkiller, and cetirizine is an antihistamine.

If you take them at the recommended doses, it should be fine. Remember to take in to consideration the other product warnings (eg. don't take while pregnant, if you have kidney disease etc).

However I assume you want to take Cetirizine because you are taking large or recreational doses of codeine and you are getting the itches.

In this case, it may be dangerous to take cetirizine with the codeine as they both cause depression of the central nervous system and their combined effect in a high enough dose would be enough to kill you. Even on their own they could kill you from respiratory arrest (you stop breathing).

Also be careful if you are taking high doses of the acetaminophen and codeine tablets. There is generally enough acetaminophen to kill you or at least do some serious damage, long before you will get high from the codeine. If you insist on taking a larger than recommended dose, at least look up cold water extraction and do this on the tablets first if you want to minimise your chances of harm.