At a secret airbase in Wilts, we found out that one of our guys was a serious cocaine user rather late in the day (when it came to crisis point)
It was a bit startling to find out that he was being treated - the Med Centre was fully aware of his problems, but it was treated as 'Medical in Confidence.' So he was still working on aircraft for a considerable period right up to when he was arrested.
'Medical in Confidence' apparently trumped letting his management know.