There is ongoing debate regarding the relative cost effectiveness of different classes of antidepressants. Although factors such as tolerability and discontinuation rates have been taken into account, there has been little consideration of the cost of overdose. In the current study we examined the cost of antidepressant overdose at four teaching hospitals over a four-week period and found that the cost of selective serotonin reuptake inhibitor overdose was less than half that of tricyclic anti-depressant overdose. The cost of overdose is often ignored and should be considered in future analyses of the cost effectiveness of different antidepressant prescribing policies in primary care.