Sulfation is an important conjugation reaction during the phase II metabolism of xenobiotics. The sulfation process which mainly occurs in the liver, increases the hydrophilicity of metabolites, facilitating their elimination from the body. Sulfate conjugation usually results in reducing the biological activity of the metabolite, but not always. Sulfation can increase the therapeutic activity of certain drugs including minoxidil sulfate, the active form of minoxidil used for the treatment of hypertension and hair loss. The sulfation reaction is catalysed by a group of enzymes called sulfotransferases (SULTs), which facilitate the transfer of the sulfate group from 3′phosphoadenosine 5′-phosphosulfate (PAPS), the universal sulfate donor, to a nucleophilic site of an acceptor molecule such as phenol (Scheme 1). [13][14] Scheme 1. Sulfation of an acceptor substrate (e.g. phenol) mediated by SULT enzyme and PAPS co-factor.