This is because most flu preparation contain pseudoephedrine which is a
sympathomimetic, and act in the opposite way to beta blockers

Basically beta blockers are often used to treat high blood pressure (other
things as well) and it is not a good idea to take pseudoephedrine when you
have hypertension because it can raise your blood pressure.

This is an ideal question for a new forum for pharmacy.  It is open to
everyone.  Why not post it there, and get professional advice?

Elaine

www.pharmacy-forum.co.uk
The UK Forum for all things Pharmacy