I have caustic soda at home, and I can say that it might be one of the most painful methods to commit suicide, probably even more so than hanging (though I'm not certain about that). Caustic soda is extremely corrosive, and if ingested, it causes severe damage to internal organs, corroding them and leading to prolonged and excruciating suffering. I've read about cases where some people, after ingesting caustic soda with the intention of ending their lives, chose to jump to their deaths to escape the unbearable pain they were experiencing.