First of all, you should make sure that you are innocent. If you are poisoned, no matter how you prove your innocence, you can't escape the imprisonment of law and self-morality in your life.

If it is someone else's poisoning or accident, you should make sure that your relationship with your roommate is very good or dull at ordinary times, prove that you have no motive to commit crimes, and then prove that you have no time to commit crimes during your roommate's poisoning. The most important thing is that you really didn't poison it.