It will take a little more altitude to put them down. After they are all asleep, turn the cabin back down to normal and turn the O2 mask deploy system back on. They usually sleep for most of the trip.
If you misjudge you could end up with a passenger who is either dead or has brain damage, guess who is going to jail then. Even if they have no damage you still open yourself and your company to lawsuits and other problems, I don't think the FAA would look favorably upon it either.