I don't know what a "designer disease" is, or if there's a definitive list out there, but perhaps repetitive strain injuries fit the bill.
I had a repetitive strain injury for over 10 years, to the extent that I had to give up my career in computing. (I've recently started again as an 80s-trained, pre-Windows, pre-Web dinosaur.)
Among the many medications offered to RSI patients (for symptoms such as depression, muscle tension, sleeplessness, constant pain) was Vioxx.
In my opinion one of the ways conversations like this go wrong is by confusing real symptoms with whether these conditions are genuinely medical. I don't mean to judge Restless Leg Syndrome either way, but if my repetitive strain injury were a purely medical condition (e.g. my carpal tunnels were unusually narrow) then learning the Alexander Technique, a behaviour-modification discipline, could not have been an effective way to get rid of it.
In the current medical culture it seems to me that "is this really a medical problem?" is not often enough asked. And then when it is asked, it's hard for patients, by now heavily invested in a medical explanation for their difficulties, not to feel they're being labelled malingerers.
Nick