I'm not Nerroon but I heard of that at the time (about a year ago, iirc). Word was that he went into rehab and when I saw him a few months later at some TVLand awards show, he looked okay, if kind of shaky. His fellow Taxi cast members seemed glad to see him and supportive, though.
I heard that Jeff had had past issues with drugs so it's probable that he had a 'slip' that was hopefully short-lived.
That is all pretty much the same story I've heard. The weight-loss show itself sounds familiar, so I am reasonably sure I came across it at one point or another. And I recall seeing Jeff on it, but I must not have watched for very long because I can't remember what he looked like.