Because nicotine from smokeless tobacco is absorbed through the mouth, it takes longer to produce an effect than if it were absorbed through the lungs. But using cigarettes and smokeless tobacco really do result in the same amount of nicotine intake.
"Youth and Tobacco: Preventing Tobacco Use among Young People. A Report of the Surgeon General." Department of Health and Human Services. Washington, DC. 33. Web.http://profiles.nlm.nih.gov/NN/B/C/L/Q/_/nnbclq.pdf