Do you mean causing it to happen earlier or to cause it to happen faster after it begins?

Yes

How fast do you want it?

Speed:

A firearm is hard to beat, but it leaves a bit of a mess for whoever finds you.

An Exit Bag[1] is another option, though, you really got to have the willpower to follow through.

Slow:

Alcohol, tobacco, STDs, Meth, Fent, you know... All the fun stuff!

[1] https://en.wikipedia.org/wiki/Suicide_bag