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Caffeine metabolic ratio of SMK, MSC, and NTC in urine, saliva, and plasma. Box plots of caffeine metabolic ratios (computed using scaled intensity of paraxanthine divided by caffeine) in (A) urine, (B) saliva, and (C) plasma show altered caffeine metabolic ratio in saliva and plasma. MSC indicates moist snuff consumers; NTC, non-tobacco consumers; SMK, smokers. *indicates .05 < P ⩽ 0.1, **indicates .001 < P ⩽ .05, and ***indicates P ⩽ .001.
