why? if someone's not on drugs, they have nothing to hide...and if they are on drugs, it doesn't really seem that they should have any privilege or right to hide that fact. i've never really understood what privacy is being invaded by simply verifying that someone isn't on drugs (i.e. breaking the law).
but, at the very least, it seems that any students working with patients should be allowed to be tested...i certainly wouldn't want to be a patient of someone using drugs...