The same testing should be applied to all high responsibility professions within transportation, emergency services, hospital, transportation.
Many would argue that this measure would be too drastic, and that persons given this high responsibility in the first place are adhering to the rules 99.9% of the time. But those 0.1% is still a whole lot of flights and hospital operations, and is a factor that should be easily removed.
Basically, if you're expected to work the day after going out on a binge, call in sick. Don't jeopardize other people's lives because you're confident that you'll do the job right, as you've done many times before.
And if he is not able to fly the plane, he should not fly it. Remember the dangers of drunk driving? Now imagine that, 11,000 Meters above the earth. But not only should they be checked for drug influence, but they should be checked for carrying drugs aswell. Most pilots would never get drunk on a plane, and those who would need to be sorted out, and detained for further investigation.
Airplane pilots should not be tested for drugs and alcohol every time they go and fly a plane. You do not expect bus divers, taxi drivers or any other profession to be tested for drugs daily, so why should pilots be tested daily? Pilots should be tested randomly just like every other profession.