To be able to predict efficacy and adverse reactions involving compounds metabolized by sulfonation, the investigators need more information on SULTs. Studies of in vivo sulfonation in humans are lacking, although they are of key importance in assessing the functional consequences of individual variation. In our current study, the investigators will start by developing an HPLC method of quantifying SULT1A1 activity using paracetamol as probe substrate and studying intraindividual variation in healthy adults. Advantages of using paracetamol as a probe substrate for in vivo phenotyping of SULT1A1 include: wide safety margin for in vivo use, easy and ready administration of the drug, significant metabolism by the enzyme of interest, short half--‐life, linear pharmacokinetics over a wide concentration range and a limited number of metabolites, quantifiable in plasma.15,24 In a subsequent study, the investigators plan to study interindividual variation in a larger sample, including subjects with chronic disease and on medication.The investigators expect to provide a valuable new tool to explore the clinical significance of variation of SULT1A1 activity, the most important SULT on drug metabolism.