Guidelines for clinical trials are rigid and important and it is inappropriate to try and cheat them.
A number of biochemical markers have been used to validate claims of nonsmoking, including measures based on thiocyanate, 4-7 nicotine, 8 cotinine, 9-11 and carbon monoxide.4, 6, 11, 12 These measures differ widely in availability, cost, and ease of administration. Measures based on nicotine have the advantage of being specific to tobacco but require expensive laboratory instrumentation. Levels of thiocyanate and carbon monoxide are much easier to determine but may be raised through exposures unrelated to smoking, such as traffic emissions and diet. Few studies have attempted to compare the various biochemical tests.