The primary objective is to investigate the effect of Lorazepam as compared to placebo on the change of the level of sCortisol between baseline (C1) and immediately before endoscopy (C2) in adolescents undergoing a gastroscopy or a colonoscopy. The investigators think that it might be possible to modulate the stress response with the administration of a benzodiazepine as soon as the children arrives at the hospital. Thus children could have a better experience of the digestive endoscopic procedure (less pain and more comfort).