I didn't read all the posts so this is probably covered but i had not seen it yet. Intoxicated pax are not allowed on an aircraft unless under direct medical supervision. So it stands to reason that becoming intoxicated on a flight would be equally as illegal though would not bring liability on the pilot. I think the PIC has the authority to end that flight and if the pax becomes a hassle then an obligation to end the flight. I read this to be alcohol and drugs both.