Don't SCRATCH!!!
I have seen adults that have had chicken pox... Nasty when they scratched, with the scars afterwards.
Don't worry about what Beagles747 said about getting hooked on drugs. It is a bit of an urban myth about being sick and getting hooked on drugs. 99.5% of the people that have been given heavy narcotics, wean themselves off the drugs naturally. When the pain goes away, they naturally lower their dosage.
Besides, if you just by chance do get hooked on the drugs, don't worry, let your doctor know. They are required to and skilled to get you off of them.
So... Use the drugs that your doctors prescribes. Let him/her know if they are to weak, or to strong. The new philosophy about pain management is to make the patient comfortable, period. Don't worry the patient about the possibility of being hooked on the drug. Because like I said before, your odds of being addicted is quite low (if you are an average person).
Also, you heal faster when you don't feel the pain. So again, talk to your doctor an make sure that you get the proper medication to be comfortable.
How do I know this? I have spent my fair share of time in the hospital. Had a nurse freak me out about being hooked on painkillers one time. Told the doctor about her. He sat down, got out the books and showed me studies. Assured me not to worry, besides it is easier to deal with the possible addiction than the pain. BTW, I never saw that nurse afterwards.