I have worked on the railways for over 20 years and about 12 years ago the government introduced legislation that made all staff aware of the need to show due diligence with regards to colleagues under the influence of drugs and/or alcohol. Management were also required to introduce a programme of random unannounced testing. There was and still is a zero tolerance policy with regards to any amount of drug taking but the limit for alcohol was just under the legal drink drive limit.
London Underground imposed a total zero limit on alcohol and dismissed a large number of staff for being drunk on duty, this despite strenuous denials from some of the staff involved. The subsequent appeals only upheld the sackings. Then it happened that a senior manager was dismissed for being under the influence of alcohol whilst on duty. The manager also happened to be tea-total and had never drunk alcohol in his life. He sought scientific advice and to cut a long story short found that the body does indeed produce natural alcohol. This was presented to an industrial tribunal and the manager was re-instated. London Underground have since amended their policy to the current statute standards and paid out thousands in compensation to it's sacked employees.
Don't know if this will help anyone or where you can find any information on the body producing alcohol but I know it does happen hence the shift in LU policy. I don't think the aviation industry has much to fear from random drugs and alcohol testing. Only those that abuse D and A should worry. If aviation follows the railway example and allows those with a problem to come forward in confidence and admit it (pre test day) and help them out, then it can only be a good thing.