Three types of hyperalgesia can occur during the postoperative period: primary hyperalgesia, which disappears with wound healing, secondary or central hyperalgesia, which can lead to chronic pain, and opiate-induced hyperalgesia. Different drugs, most of which are NMDA receptors antagonists, are used to decrease or prevent the risk of central or opiate-induced hyperalgesia. However, it is difficult to determine whether they are really effective and at which dosage: the results of most published studies are difficult to interpret because of methodological problems. The two most frequent of those are: absence of objective measurement of secondary hyperalgesia and difficulties targeting an at risk population.