This randomized 2x2 factorial intervention trial administers 8 weekly cognitive behavioral therapy (CBT) sessions (yes/no) and 4 bi-weekly active whole-body hyperthermia (WBH) sessions (yes/no) to adults aged 18 years or older with major depressive disorder (MDD).

Major Depressive Disorder afflicts more than hundreds of millions of people worldwide and is the leading cause of life years lost to disability. Current treatments have important limitations in efficacy and, in the case of medication, substantial side effects. There is thus a compelling need for additional effective, well-tolerated treatments. One such potential treatment is whole-body hyperthermia (WBH). The investigators hypothesize that WBH may be particularly effective in combination with cognitive behavioral therapy (CBT), an established treatment for depression. This randomized 2x2 factorial intervention trial administers 8 weekly cognitive behavioral therapy (CBT) sessions (yes/no) and 4 bi-weekly active whole-body hyperthermia (WBH) sessions (yes/no) to adults aged 18 years or older with major depressive disorder (MDD). This work holds important promise to improve the treatment of depression and to advance understanding of the role of integrated mind-body therapies for mood disorders.

Inclusion Criteria:

• 18 years or older
• Able to read and speak in English
• Able to understand the nature of the study and able to provide written informed consent
• Current major depressive episode of at least 2 weeks duration as assessed by the Structured Clinical Interview for DSM-5 (SCID) and a Patient Health Questionnaire - 8 (PHQ-8) score of 10 or greater at screening
• Willing to use a form of pregnancy contraceptive (e.g., barrier methods such as condoms, oral contraception, or other birth control type) if assigned female sex at birth and premenopausal
• Able to lie supine for 2 hours in a sauna device
• Access to the internet via computer, smartphone, or tablet

Exclusion Criteria:

• >30% reduction in BDI-II score between Screen #1 and Screen #2 (conducted ~1 week after Screen #1)
• Suicide attempt in the past 12 months defined using the SAMHSA suicidality question during the clinician-administered interview or active suicidal ideation as indexed by a score of 3 on the BDI-II suicidality item during the clinician-administered interview
• Any of the following medical conditions: cardiovascular disease (other than controlled hypertension), seizure disorder, history of cerebrovascular accident (CVA) or other serious neurological condition (e.g. Parkinson's disease, multiple sclerosis, or dementia), current neoplasia, any active enclosed infection (e.g. dental abscess, joint infection), hemophilia or other cause for excessive bleeding (e.g. platelet disorder), or other medical condition that in the opinion of investigators may increase the risk of WBH
• Comorbid psychiatric conditions or history of comorbid psychiatric conditions that might better explain depressive symptoms, including schizophrenia, schizoaffective disorder, Bipolar Disorder I, Obsessive Compulsive Disorder, Anorexia Nervosa, Bulimia Nervosa, Alcohol Dependence, or Drug Dependence
• Known hypersensitivity to hyperthermia and/or infrared exposure
• Inability to fit into the sauna device
• Breast implants
• Pregnancy, active lactation or intention to become pregnant during the study period
• Use of any medication that might impact thermoregulatory capacity, including: Diuretics, barbiturates, beta-blockers, antipsychotic agents, anti-cholinergic agents or chronic use of antihistamines, aspirin (other than low-dose ASA for prophylactic purposes), medication prescribed for the treatment of depression (antidepressant medication [ADM]) including but not limited to: selective serotonin reuptake inhibitors [SSRIs], Serotonin and norepinephrine reuptake inhibitors [SNRIs], Monoamine oxidase inhibitors [MAOIs], Tricyclics [TCAs], and atypical antipsychotic and antidepressant medications (participants must have been free of these medications for at least 4 weeks), antibiotics (past 14 days), pain medication (opioids) due to procedure, e.g., dental procedure (past 14 days), Emergency contraception pill (past 14 days), or any other medication that in the judgment of the PI would increase risk of study participation or introduce excessive variance into physiological or behavioral responses to WBH
• Recent use (multiple consecutive doses) of: non-steroidal anti-inflammatory drugs (NSAIDs), systemic corticosteroids, cytokine antagonists
• Regular use of any nicotine products, including cigarettes, vapes, chewing tobacco, or other forms of nicotine (if use is not regular, must be willing to refrain for 24 hours before and 24 hours after WBH session)
• Unwilling to refrain from using marijuana products and alcohol for the 24 hours before and 24 hours after WBH session
• Unwilling to refrain from heavy exercise on the day of WBH sessions
• Unwilling to refrain from engaging with sauna, hot yoga, cold plunges, cryotherapy, and hot tub/jacuzzi outside of study (prospective participant must not have engaged with any of these activities for 30 days prior to their baseline study visit).
• Has begun new psychotherapy treatment in the prior 6 weeks

The final IPD dataset will include self-reported demographic data, other self-reported data (e.g., subjective mood measures), and clinician-assessed data (e.g., depression diagnosis status).

Beginning 3 months after the publication of results and unending.

Data will be accessible via the Vivli platform. To access IPD arising from this project, users must complete the Vivli data request form and sign the Vivli Data Use Agreement, which limits subsequent use to the terms of the approved request and requires that users maintain data security, and refrain from any attempts to reidentify research participants or engage in any unauthorized uses of the data. In order to get access to the data, the user must submit a valid scientific question, include a statistical analysis plan, and complete all required fields on the Vivli data request form. Vivli will review the data request for completeness. Anyone who has submitted an approved data request and signed a data use agreement on Vivli will be given access to the data. Vivli will then make the data available, without cost, to users for a set period of time. Vivli will maintain storage and access of the data for as long as it maintains scientific utility.

Study clinician-assessors will perform clinical interviews and provide CBT, but will be masked to the participants' WBH condition (yes/no).