There is a vast body of criminal case law against killing or poisoning people whether or not death immediately ensures. The Carmichael case is especially apt as it bans providing a person a mind-altering drug impacting behavior. Tobacco is a classic mind-altering drug impacting behavior. Cigarettes' vast combination of poisons including nicotine, carbon monoxide, and rat poison, increase blood pressure, constrict blood vessels, make capillaries fragile, and inhibit clotting. For more information, see standard medical references on the substances.
Cigarettes emit vast quantities of carbon monoxide and hydrogen cyanide.
Carbon monoxide and hydrogen cyanide are the gas chamber poisons that Nazis used to kill about six million people.