You can kill yourself with Aspirin, in fact I thought that Aspirin was the #1 choice for that (without research). In any case, take too much and you are dead - I think not because of stomach ulsters, but because of bleeding in the brain. Again, that's just from memory, but google for it and you'll find some negative side effects. I think there is also a problem in combination with other stuff, for example grape fruit juice.

(Edit: Googling for "aspirin suicide", find it in top 20 list of suicide methods http://wantdeath.blogspot.de/2011/07/method-5-of-suicide-asp... )