How long has toxicology been around?

About 500 years, in the 16th century, a guy named Paracelsus first realized that literally anything can kill a human if it's taken in to big a quantity . He coined the phrase "The dose makes the poison"

But forensic toxicology wasn't invented until the 1840's when chemist Mathieu Orfila proved in court that Marie LaFarge poisoned her husband with Arsenic