Drugs in swimming

Question
Have any former East German or Chinese swimmers had to give up Olympic medals after admitting to steroid use after the medals were awarded? If not....why not?

Answer
Marylka--
I know that none of the East German women from the 70's have lost their medals, even though it is pretty obvious that steroids were probably used.  There just wasn't the testing technology to prove it.  There has only been a couple of chinese swimmers who have been stripped of their medals, but that was world championship not olympic medals.