Trying to classify a nicotine product as a dietary supplement was attempted in 2005 and failed.
The FDA deemed that nicotine "does not meet the definition of a dietary supplement" and the "mere presence of nicotine in foods such as cauliflower, eggplant, potatoes, and tomatoes, without any evidence that these foods were promoted for their nicotine content, does not constitute 'marketing' nicotine as a food or dietary supplement" under the Dietary Supplement Health and Education Act.
According to the FDA, nicotine is "an article authorized for investigation as a new drug" and "21 U.S.C. 321 (ff)(3)(B) states that the term 'dietary supplement' does not include 'an article authorized for investigation as a new drug...for which substantial clinical investigations have been instituted and for which the existence of such investigations has been made public, which was not before such approval, certification, licensing, or authorization marketed as a dietary supplement or as a food...."
"Nicotine was authorized for investigation as a new drug on December 2, 1987. To the best of FDA's knowledge, nicotine was not marketed as a food or dietary supplement before the date nicotine was authorized for investigation as a new drug."
http://www.ahpa.org/Portals/0/pdfs/06_0629_FDA_NicLite_ltr.pdf