A pilot study of plasma caffeine concentrations in a US sample of smoker and nonsmoker volunteers.
de Leon J, Diaz FJ, Rogers T, Browne D, Dinsmore L, Ghosheh OH, Dwoskin LP, Crooks PA. A pilot study of plasma caffeine concentrations in a US sample of smoker and nonsmoker volunteers. Prog Neuropsychopharmacol Biol Psychiatry. 2003 Feb; 27(1):165-71.