This study will investigate the pharmacokinetics of acetaminophen in morbidly obese patients versus normal weight patients. Specifically the different metabolic pathways of acetaminophen in morbidly obese adults will be investigated; glucuronidation, sulphation and CYP2E1 (cytochrome P450 2E1) oxidation

Inclusion criteria for morbidly obese patients:

• BMI > 40 kg/m2 undergoing bariatric surgery.
• Patients between 18 - 60 years old
• ASA physical classification of II or III
• All racial and ethnic groups will be included

Inclusion criteria for control group:

• BMI between 18 and 25 kg/m2 undergoing general surgery
• Patients between 18 - 60 years old
• ASA (American Society of Anesthesiology) physical classification of I, II or III
• All racial and ethnic groups will be included

Exclusion criteria for all study arms:

• Renal insufficiency
• Liver disease
• Patients with Gilbert-Meulengracht syndrome
• Chronic alcohol intake or use of alcohol within last 72 hours
• Pregnancy or breastfeeding
• Patients who are treated with drugs know to affect CYP2E1 and UGT (UDP glucuronosyltransferase)
• Diabetes mellitus type II patients
• Smoking
• Acetaminophen intake before the study (24 hours before study)