The director of the Mayo Clinic Nicotine Dependence Center says Minnesota's tobacco trial will prove to be one of the most significant public health developments of the latter part of the 20th century. Dr. Richard Hurt was the state's first witness in the case. He testified nicotine is a drug and said tobacco companies conspired to hide its addictiveness. Dr. Hurt told Minnesota Public Radio's Brent Wolfe the trial is as important as any warning issued by the surgeon general.