As I understand he's swapped the real pills with ibuprofen placebos. I'd have to watch again more closely as far as how careful he was in swapping them out but I thought he put in as many as he took out.
But the plan isn't to kill him with a poison pill (which would show up in an autopsy I think) but to prevent him from getting his daily dose of medicine. It won't kill him first pill but omitting his intake would do damage over the long term, building up until he drops dead, if it is a pill he needs to take to regulate heart or lung function etc.