well, anything with Codeine in it has be treated with respect, and a 30mg dose is a fairly big dose.
But, so longa s you dont overdose on them, stick withing th limits and go back to your doctor if you have any problems with them.
The Doc generally knows what they are doing, so i'd just trust them.
From a personal POV, i've just been taking a Codeine Phospate 30mg, and all i would say is, try to time it so you dont have to do anything afterwards for a little bit, because mine occasionally knocked me for 6 or just made me fall asleep, but i don't know the exact differance between Dihydrocodeine and Codeine Posphate, so sorry about that.
just my POV, but if in doubt, always go see the doctor if in doubt.
hope you get better soon mate,
J