Well at the bare minimum you must possess a bachelors degree in either physics, chemistry,biology, forensic science, or any other closely related field.
But if you want to start out with a higher pay a masters in toxicology/forensic toxicology is suggested, however if you persist in your studys and obtain a Ph.D you can start as the head forensic toxicologist and make alot of money $100k + and if you become board certified even more.