I have a friend who has travelled to the U.S, Canada, UK, and Australia a few times. He is prescribed the painkiller oxycodone (Oxycontin) by his GP and an anti-anxiety medication, diazepam (Valium) by his psychiatrist.
He says that he takes it normally but I know that he's teetering towards addiction as he now takes an added dose for sleep as well. He's taken these on flights and slept deeply as well as totally forgot his experience. Knowing that he'll build tolerance to it and have to take larger doses, I imagine there's a time that will come when hill suffer an overdose particularly as these are both CNS depressants.
If he were to take these on a flight and then become unconscious to the point where the crew couldn't arouse him from his sleep, would he get charged for disrupting the flight when he lands? I believe that a pilot would have to deviate the plane from its original destination.