active ingredient: glycyrrhizin
Licorice does double duty in a cigarette, both adding a sweet, desirable flavor and by providing the chemical glycyrrhizin which stimulates the airways in the lungs to open wider. [3]
"'As far as liquorice is concerned, the smoothing effect of this is probably due to the Glycyrrhizin present which is renowned for its demulcent therapeutic property.[1] Glycyrrhizin is an effective demulcent [soothes or protects irritated mucus membranes]; it is also a bronchodilator and carcinogenic when burnt.[2]"[3]
Licorice extract can be up to 0.8% of the weight of a cigarette.[4]
An excellent resource on what is added to cigarettes and why: http://www.ash.org.uk/?additives
[1] tobacco company document: British American Tobacco (BAT) January 15th, 1963, Additives Australia, FN G443, BN 102630086-102630092
[2] book?;Connolly, G. and Lympers, D. 1998 summary of evidence, findings and conclusions concerning the nicotine yield ratings of and added constituents of cigarettes and smokeless tobacco products. The Massachusetts department of public health tobacco control programme, p 281.
[3] online report: Action on Smoking and Health, Tobacco additives: cigarette engineering and nicotine addiction, July 1999. Section 4. -see: http://www.ash.org.uk/?additives
[4]website: Phillip Morris USA, "tobacco ingredients in all brands" - see: http://www.philipmorrisusa.com/downloads/composite_list.html