In the end it was the headaches that did him in. Had he been asked to guess, he would have said an overdose of painkillers. For better or worse, the painkillers were very safe. It was all but impossible to die from an acute overdose, though long term overuse did cause chronic issues.
He did not last long enough to see what sort of long term effects twenty tablets a day would do.
People joked that he had tried to lobotomize himself, but that was putting it too politely. Lobotomies involve neither the opening the skull nor significant loss of blood or other tissue.
–From Proceedings of the 3rd Congress on Trans-temporal Information Science, “Effects of Unaided Reception of Trans-temporal Messages on Mid-Twenty-first Century Human Minds”