The sudden hypokalaemia was caused by a massive intracellular shift of potassium in response to the hyperinsulinemia, triggered by the intravenous administration of glucose.<h4>Main lesson</h4>To our knowledge, we are the first to document a significant rise in endogenous insulin production in a hypoglycaemic patient presenting with tramadol intoxication. Here, INS is linked to hyperinsulinism.