I frequently see vapers arguing that e-cigarettes are not a "tobacco product," because they do not actually contain tobacco. They argue that nicotine e-cigarettes are not the same as tobacco or smoking cessation products and should have a classification all of their own.
However, nicotine isn't regulated in the U.S. by what form it takes, but instead by "intended use."
If the nicotine is contained in a product with an "intended use" as a smoking cessation or other treatment, it is then regulated as a "drug" and must go through clinical trials, studies, etc., and the product must meet strict manufacturing protocols before release to the public. If the nicotine is contained in a product with an intended use of "recreational" (ie. intended for human consumption but not as a treatment of any kind) it is regulated as a tobacco product. (A third classification is a pesticide, but that form of nicotine is not allowed for human consumption.)