The primary aim of this study is to investigate the effectiveness of whole-body hyperthermia in comparison to wait list on depressive symptom severity in patients with mild to moderate depressive disorder currently not under psychotherapeutic or antidepressant drug treatment.

Secondary aims included further quality of life outcomes, immunological parameters, and tolerability/safety of the hyperthermia.

Inclusion Criteria:

• Unipolar depression (diagnosed according to the DSM-IV)
• Mild depression: 8-16 points on the HAMD-17 or moderate depression: 17-23 points on the HAMD-17

Exclusion Criteria:

• Current psychotherapy
• Antidepressant drug treatment in the last 4 weeks before study inclusion
• Participants who did not respond to prior antidepressant drug treatment, electroconvulsive therapy, or sleep deprivation (therapy-resistant depression)
• Acute suicidality
• Prior treatment with whole-body hyperthermia
• Contraindications to hyperthermia treatment: acute or feverish infections, severe cardiovascular diseases (e.g. angina pectoris, heart failure, thrombosis, bleeding diathesis), severe gastrointestinal diseases (e.g. renal insufficiency, hepatitis, liver cirrhosis, peptic ulcer), severe neurological diseases (e.g. epilepsy, multiple sclerosis, cerebrovascular malformations or brain tumors), severe endocrine diseases (e.g. hyperthyroidism), or oncological diseases without remission
• Participants taking anti-inflammatory or immunosuppressive drugs
• Participants with severe psychiatric comorbidities (e.g. schizophrenia, schizoaffective disorder, bipolar disorder, dementia, ADHD, obsessive-compulsive disorder, PTSD, alcohol or drug addiction)
• Women during pregnancy and breastfeeding
• Lack of ability to consent