It is not unusual these days for the hospital to assist in the passing of someone terminally ill, by giving them more morphine than they can handle in their weakened state. This is usually done at the family's request. No one uses the term "lethal dosage" but everyone knows what is being done.
If I am ever lying in a hospital bed, suffering and beyond any hope of recovery, I hope someone does me that kindness... and not having to ask is a kindness as well. People who are past any chance of recovery or of ever leaving the hospital should not be forced to linger on in pain because their family lacks the moral courage to ask for the maximum morphine dosage.