Insufficient evidence exists for a viable choice between long and short-term psychotherapy in the treatment of psychiatric disorders. This study compares the effectiveness of long-term and short-term psychodynamic psychotherapy in the treatment of mood and anxiety disorders.

The Helsinki Psychotherapy Study is a randomized clinical trial based on 229 psychiatric outpatients from the Helsinki area, with depressive or anxiety disorder. The patients were randomly assigned to either long-term or short-term psychodynamic psychotherapy. The patients were followed for 3 years from start of therapy. Primary outcome measures were depressive symptoms, measured by the self-report Beck Depression Inventory (BDI) and the observer-related Hamilton Depression Rating Scale (HDRS), and anxiety symptoms measured by the self-report Symptom Check List, Anxiety scale (SCL-90-Anx) and the observer-related Hamilton Anxiety Rating Scale (HARS).

A statistically significant 49-64% reduction of symptoms was noted for the 4 outcome measures during the 3-year follow-up. Short-term psychodynamic psychotherapy was more effective than long-term psychodynamic psychotherapy during the first year of follow-up showing 15%-27% lower scores for the outcome measures. During the second year of follow-up no significant differences were found between the two psychotherapy groups. After 3 years of follow-up, long-term psychodynamic psychotherapy appeared to be more effective with 14%-37% lower scores of the outcome measures.

Short-term psychodynamic psychotherapy is more effective than long-term psychodynamic psychotherapy during its treatment period but in the long run long-term psychotherapy is more effective than short-term psychotherapy.