Cotinine
Cotinine is an alkaloid found in tobacco and is also a metabolite of nicotine[1]. Its presence in saliva, blood or urine is (ab)used as a presumption of nicotine consumption, whether by smoking tobacco products or by using smoking cessation products that contain nicotine (gum, patches, e-cigs,) and such testing is used to screen employees in companies that ban employees from smoking at all.
It can also be present in those who have had exposure to second hand smoke in levels that cannot be differentiated from that of a light smoker.
Cotinine is also sold as a drug in its own right as an antidepressant under the brand name Scotine[2].
It is also present in other plants such as those in the family Solanaceae, including tomatoes and potatoes, and in some black teas[3]
Because of the potential for exposure to nicotine by way of these routes [i.e. by eating or drinking], the use of urinary cotinine as a biomarker of exposure to environmental tobacco smoke may be compromised.[3]