He took barbiturates/pentobarbital (N). I think he had access to this because he was a member of Exit, one of the only (to my knowledge) people under the age of 50 who were ever allowed to join. I'm not sure how he managed to convince them to allow him to become a member, since many other younger people with chronic illnesses have been denied. Perhaps it was due to how famous he was in the media, and also the fact that his parents fully supported his wish for euthanasia.