That or maybe falcons. Train birds of prey to knock drones out of the sky. Might not be safe for the bird, depending on the type of drone. I wonder if falcons are smart enough to make that sort of judgement call themselves..
Edit: though I guess there might be some simple countermeasures
Or the US could just go with something that actually works, like the Portugal system of scrapping all drug laws. After fifteen years none of the imagined horrors have come true, addiction has dropped to half the previous value, law enforcement costs have gone down, and things are generally better.
People look at Portugal, see that the facts contradict their imaginary scenarios, and deny the facts, but that doesn't change them.
For that reason, I think the ideal solution would involve capturing the drone somehow, maybe with a net of some kind. Innocent drones could be marked with contact information, allowing them to be returned to their owner in the event that they are mistakenly captured.
As an added benefit, harmlessly capturing the drone would provide more useful evidence for the police investigating drug crimes.
But most modern AA weapons have tremendous velocities and are often explosive. Even after losses due to air resistance, AA shrapnel can come with with lethal velocities. I was told by somebody I trust that the Baghdad suffered more damage in financial terms from AA fallout than the actual US air strikes in the first US/Iraq war.
The counter-countermeasure, of course, is to start making "deliveries" to random people, and tie up law enforcement by compelling them to arrest innocent parties.