There's a persistent urban legend concerning the herb, goldenseal: take it before a urine test and you'll get false-negative results for a variety of recreational drugs. Disappointingly for those who try, goldenseal won't mask drug residues in the blood. The idea came from Stringtown on the Pike, a novel published in 1900 by plant pharmacist John Uri Lloyd. In the book, goldenseal causes a false-positive result for strychnine poisoning. (Podcast: The Plant Detective , 9/6/14)