I definitely wouldn't count on it as being strong enough. Just get heroin, or even make poppy seed tea (Simply Nutz is the favored unwashed brand and you can get it via Amazon prime, I've done it), which you could reduce to a more manageable level. It can contain a surprising amount of morphine and other alkaloids, people have overdosed on it.
The problem is that if you feel great and it alleviates your pain/suffering you may find it much harder to go through with the act, making it a good test of whether you genuinely want to die.