A lot of thread drift here... all fascinating, but the question that was asked was this:
I've told my GP about my drug use, so will that come up on my medical when applying to airlines if I don't mention it?
I would hope that the answer to that question is an unqualified "NO". If the doctor/patient confidentiality principle is undermined by employer or government department interests then the ability of our society to address reform will be destroyed to our communal detriment.
The interesting question that follows is this: for employment with most airlines you will be interviewed/examined by a "Company-appointed DAME/Medical examiner" as part of you recruitment process. If you choose to lie to this person you may expose yourself if in a future incident investigation your past becomes known and was not disclosed.
So you are in a tricky position. The longer the elapsed time between notified drug use and the time of your application would probably diminish the influence on your application. If, as you say, you are 19 years old and you last used illicit drugs 2 months ago, I would say an employer would flick you like a fly on the face. Alternatively, if you had many years of gainful employment with good references since your "silly youthful drug use as an 18 year old" most employers would put the emphasis on your other attributes, and only small consideration would be placed on that issue.
Should you lie? I don't think anyone would recommend that, that is a risk analysis only you can answer but you need to consider the ramifications should it "come out in the end" after some incident.
Put yourself in the position of Chief Pilot of an Airline for a moment - would you risk putting a pilot with "known drug history" in the hot seat of an airliner carrying hundreds of people? If an incident occurred and the media got hold of the pilot's history, would you want to be defending that?
Plenty of people hide stuff, the measure of what and when is, at the end of the day, up to you - so be careful and be wise (these are attributes of a good pilot, after all.... )
