Adjunctive Vitamin D in the Treatment of Non-remitted Depression

Inclusion Criteria: Patients who meet the following criteria are eligible for enrolment in this trial: 1. Men or Women aged 18 to 65 (extremes included) who are out-patients 2. Patients with a primary diagnosis of Major Depressive Disorder (MDD) according to the DSM-IV-TR criteria (16), confirmed using the Mini International Neuropsychiatric Interview (MINI) 3. Patients who have failed to respond to treatment with a single pharmacological antidepressant agent at an adequate dose as defined by a lack of remission from the current depressive episode (score of 7 or less on the Hamilton Depression Scale) after eight weeks of treatment 4. On the basis of a physical examination, medical history and basic laboratory screening, the patient is, in the investigators opinion, in a suitable condition 5. Willing and able to attend study appointments in the correct time windows Exclusion Criteria: Patients meeting one or more of the following criteria cannot be selected for inclusion: 1. Any other Axis I disorder that was a primary disorder in the past 6 months. Co-morbid anxiety disorders will be permitted as long as MDD is judged to be the primary diagnosis. 2. Current or past mania or hypomania or a mixed mood disorder phase suggestive of a bipolar mood disorder as defined by the DSM-IV-TR (16) 3. Current or past psychotic disorder 4. Diagnosis of a mental retardation, dementia or other cognitive disorder 5. Current or past alcohol or drug use as defined in the DSM-IV-TR (16) in the last six months 6. Commencement of formal psychotherapy 30 days prior to Screening (formal psychotherapy for study purposes includes Cognitive Behavioural Therapy (CBT) or acute CBT treatment in individual therapy) 7. Current use of psychiatric medication other than the antidepressant to which the patient failed to show sufficient response. Short half-life hypnotics (anxiolytics) will be allowed p.r.n. in the evening for the treatment of insomnia 8. Patient using herbal or nutritional treatments judged to have anti-depressant effects unless they have discontinued its use with their physician's consent more than 2 weeks prior to entry into the study 9. Clinical interpretation of apparent suicide risk 10. Supplementation of vitamin D \>200IU per day in the past 6 months 11. Baseline serum vitamin D of \>150nmol/L 12. A history of parathyroid disease or kidney stones 13. Pregnant or breast-feeding females 14. Serious medical illness: Liver or renal insufficiency, cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurological, infectious, neoplastic or metabolic disturbance, diabetes, dyslipidemia and hypertension;or in the judgment of investigator as not being appropriate for the study on medical grounds 15. The patient is, in the opinion of the investigator, unlikely to be able to comply with the clinical trial protocol, or is unsuitable for any other reasons.