['Patients receiving lamotrigine therapy frequently use paracetamol concomitantly. While one study suggests a possible, clinically relevant drug-drug interaction, practical recommendations of the concomitant use are inconsistent. We performed a systematic pharmacokinetic study in healthy volunteers to quantify the effect of 4\xa0day treatment with paracetamol on the metabolism of steady-state lamotrigine.', 'Twelve healthy, male volunteers participated in an open label, sequential interaction study. Lamotrigine was titrated to steady-state (100\xa0mg daily) over 36\xa0days, and blood and urine sampling was performed in a non-randomized order with and without paracetamol (1\xa0g four times daily). The primary endpoint was change in steady-state area under the plasma concentration-time curve of lamotrigine. Secondary endpoints were changes in total apparent oral clearance, renal clearance, trough concentration of lamotrigine and formation clearance of lamotrigine glucuronide conjugates.', 'Co-administration of lamotrigine and paracetamol decreased the steady-state area under the plasma concentration-time curve of lamotrigine by 20% (95% CI 10%, 25%; P\xa0<\xa00.001) from 166 to 127\xa0μmol\xa0l(-1) . Concomitant administration of paracetamol increased the formation clearance of lamotrigine glucuronide conjugates by 45% (95% CI 18%, 79%, P\xa0=\xa00.005) from 1.7 to 2.8\xa0l\xa0h(-1) , while the trough value of lamotrigine was reduced by 25% (95% CI 12%, 36%, P\xa0=\xa00.003) from 5.3 to 3.9 μmol\xa0l(-1) .'] Does paracetamol decrease steady-state exposure to lamotrigine by induction of glucuronidation in healthy subjects?