Lots of people find them very effective for pain relief but they can also cause some nasty side effects I'm afraid. My friend when she tried them felt very very sick and never took another dose and another friend was so dizzy and spaced out she could not move and again never took another dose.
I can take them like smarties and they have no effect whatsoever on me as I am one of 10% of the population who lack an enzyme for metabolising pain relief which is a reall
I have same trouble with codeine and dihydrocodeine.
I hope you are one of the lucky ones. just bear in mind that they could give you some strong side effects so you don't take them just befor eyou drive or something!