Critically ill patients who are mechanically ventilated may require prolonged administration of sedatives and analgesics. Their prolonged use has been associated with withdrawal symptoms upon rapid weaning in critically ill patients. These withdrawal symptoms may be associated with adverse clinical outcomes. Although well studied in the paediatric population, little is known about the epidemiology, risk factors and optimal screening methods in adults. Studying this problem is essential as we strive to develop proper weaning strategies.