Forgive me for copying my post from another "seed thread" in here, but it is important to me, that people stop contemplating these methods. (Except if you are a masochist and you want to make yourself suffer more than ever before):
!!! Never ever try to kill yourself with any natural poison or venom, although it might be the end, which you so desire, but it will be the most horrific thing you will have to endure !!!
If you really wish to go for soft methods (hard methods: hanging, jumping, suicide by train or gun...) then try to go for natural toxins at least, like H2S! Or travel to Australia and get f*kd by a box jellyfish, preferably Chironex fleckeri ! Its venom is probably one of the fastest acting venom on this planet and can kill you, if untreated, within 5-20 mins. It will also hurt like hell but all other poisons and venoms will usually let you suffer for ~ 6 - 24 hours.