Prior to inclusions, patients will have to have candida infection ruled out. Laboratory examination will be performed and serum levels of iron, ferritin, folate, vitamin B12 and glucose will be measured. Any abnormalities in these levels will lead to exclusion. If the patient is using an antidepressant or anxiolytic, they must have been on it for at least 6 months with no change in dosage. Resting salivary flow rates will be measured to rule out patients with hyposalivation (<0.1ml/min).