This multi-centred study will be conducted at two centres. The design will be an open label, flexible-dose study. This investigation will evaluate the efficacy of Desvenlafaxine monotherapy for patients who meet diagnostic criteria for dysthymia.

Primary objective: To investigate the efficacy, safety, and tolerability of open-label desvenlafaxine monotherapy in dysthymic subjects.

Secondary objectives: To evaluate the efficacy of desvenlafaxine on clinical measures relating to improvement of depressive symptoms, quality of life and occupational functioning.

It is hypothesized that Dysthymic subjects will show significant improvement in depressive symptoms after 8 weeks of treatment with desvenlafaxine. There will be significant improvement in measures of quality of life and stress coping at end of treatment, compared to Baseline. There will also be significant improvement in measures of occupational functioning at end of treatment, compared to Baseline.

Inclusion Criteria:

• Male and female patients between 18-65 years.
• Primary diagnosis of Dysthymic Disorder, as defined by DSM-IV criteria (300.4).
• MADRS score ≥15 at Screening and Baseline.
• Supportive therapy, and use of zopiclone for sleep and low-dose benzodiazepines on an as needed basis for anxiety, is allowed at any time.
• Written informed consent

Exclusion Criteria:

• Co-morbid diagnosis of any other Axis I disorders (other than anxiety disorders such as Generalized Anxiety Disorder, Social Anxiety Disorder and Post-traumatic Stress Disorder, provided that Dysthymic Disorder is currently the diagnosis).

• Meet DSM-IV criteria for a current episode of major depression within two months prior to screening or who have received treatment for a major depressive episode within six months prior to screening.

• Substance abuse or dependence including alcohol, within 6 months prior to screening.

• Patients on the following prohibited treatments:

  1. Psychotropics such as other SSRIs, other SNRIs, lithium, sibutramine, tramadol, St. John's Wort, within 2 weeks of randomization
  2. Agents that impact significantly on serotonin metabolism (e.g. MAOIs, tryptophan, triptans) within 2 weeks of randomization

• Have received physical therapies for depression (e.g. ECT, rTMS) within the 3 months prior to randomization.

• Previous non-response to a therapeutic trial of desvenlafaxine (at least 50 mg/day for 2 months).

• Clinically significant abnormalities in hematology, clinical chemistry, urinalysis or ECG at the screening visit, as judged by the Principal Investigator.

• Presence of medical or psychiatric condition deemed by the Investigator to interfere with study procedures or endpoint data.