I have been taking 6-8 30mg tablets a day for the past 6 months since being diagnosed with Fibromyalgia. I was first prescribed Tramadol, which had little effect, so my GP switched me to DHC.
As with all prescription drugs, there can be side effects. They sometimes make me feel light headed, and they do make concentration more difficult, though not impossible. However, the positives far outweigh the negatives. DHC has allowed me to carry on with my job by dulling the pain I experience sufficiently. It does not get rid of it completely - to do that would require a far higher dose with more severe side effects.
Codeine is an addictive substance if abused. When my pain is bad, I take it. When it's not, I don't. I don't treat it as a lifestyle drug, unlike others I've encountered - you should use it only when you need to, not when you feel like it. If you follow these rules, it can be a life saver.
Again, as with all drugs, some people have bad reactions to it. DHC is a strong painkiller, and does cause adverse reactions in some people. If this is you, stop taking it and ask your GP for something else - that's what I did with Tramadol.
Don't be frightened by the scare stories you may read - if you have a genuine need for DHC, it can mean the difference between an acceptable quality of life and no quality of life. For that, I am more than willing to put up with the side effects.