ON A SUNNY DAY LAST JULY, Dee Chiplock hoisted herself into her Honda Odyssey, equipped with hand controls instead of foot pedals. She pulled away from her Saginaw, Michigan, home and headed toward the Canadian border. On the seat next to her was a plastic bag containing a deadly dose of prescription pain medication and tranquilizers. Eight months earlier, the 40-year-old mother of two boys had been diagnosed with ALS, a degenerative nerve disease with no known cure.

[ . . . ]