 While treating depression, significant numbers respond poorly to anti-depressants; one cause is vitamin B12 deficiency. The investigators are conducting an open label randomized controlled trial to investigate difference in response to SSRI monotherapy alone versus SSRI and intramuscular B12 replacement in people with low-normal B12 levels. 300 participants will be allocated to each arm of intervention at out patient clinics of the department of Psychiatry at Aga Khan University Hospital, Karachi Pakistan. Baseline and 3 month measurement of depression will be on Hamilton Rating Scale for Depression Urdu version and response rates compared. 