Th purpose of this study is to determine whether dual psychological and pharmacological treatment is superior to either mono-therapy alone in the treatment of postnatal depression.

Inclusion Criteria:

• Women with an infant > 2 months and < 8 months of age
• Infant born after a full-term pregnancy
• Infant born with no congenital abnormalities
• Diagnosis of depression with postnatal onset according to the Diagnostic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV).

Exclusion Criteria:

• positive serum pregnancy test;
• concurrent psychiatric disorder (excepting co-morbid anxiety);
• recent history of antidepressant usage (within the last month);
• history of major allergy or drug allergy;
• history of substance abuse;
• prior non-response to sertraline, or prior non-response to adequate trials of two selective serotonin reuptake inhibitors (SSRIs);
• predisposition to headache, migraine or nausea;
• tobacco habit in excess of 10 cigarettes per day;
• caffeine consumption in excess of 6 cups of coffee/tea or cola-flavoured drinks per day;
• ongoing dental work;
• extreme levels of depression (psychotic);
• suicidal intent;
• participation in any medical trial within the previous three months;