Interestingly, perhaps thought should be given to introducing carefully designed, short simulator sessions that could reveal functional and mental shortcomings immediately before every flight. They need not be longer than 10 minutes or so, and if failed, require either a follow up blood test or a programme of retraining.
So let me do some calculations. BA has circa 4,500 pilots. So let's say, conservatively, 30 minutes required to get to the simulator, get it configured and then carry out the exercise. That makes 2,250 hours of simulator time required to cover every pilot for just one flight each. Plus someone to operate the simulator and assess the performance.
What I find quite extraordinary in this thread is the draconian proposals to address a virtually non-existent problem, certainly as far as crews based in Europe and the USA are concerned. I cannot speak for other areas.
Much like the proposals to reduce the blood/alcohol limit for drivers in the UK will not actually stop or reduce the number of people prosecuted any changes to the existing regime will have little or no effect. It will just make life a little less tolerable for those who behave responsibly, those with an alcohol problem will continue whatever the limits whether it be driving or any other walk of life.