Inclusion Criteria:
* Age Range: 18-99 years old.
* Patients with a current major depressive episode according to DSM-5, in a stable phase (defined as at least 4 weeks without significant changes in antidepressant treatment and no psychiatric hospitalizations in the previous 8 weeks) and with moderate or greater severity, as indicated by a total score of
* 20 on the Montgomery-Åsberg Depression Rating Scale (MADRS).
* Insomnia disorder confirmed according to DSM-5
* Insomnia Severity: Insomnia Severity Index (ISI) score = o \>15.
* Medication Stability defined by :
* Stable doses of antidepressants, mood stabilizers, or antipsychotics for at least 1 month prior to baseline (T0).
* Melatonin, Benzodiacepines, sedative antidepressants or sedative antipsychotics use for insomnia should follow a wash out protocol described below.
* Informed Consent: Ability and willingness to provide written informed consent.
* Acceptance of Protocol Requirements: Agreement to adhere to all scheduled visits, treatment plans, and study procedures.
Exclusion Criteria:
* Other Current Psychiatric Disorders: Any current psychiatric disorder other than major depressive disorder (e.g., active psychotic disorders, mania, hypomania, acute schizophrenia, schizoaffective disorder).
* Use of Non-Permitted Sleep Medications: Concurrent use of melatonin, benzodiazepines, sedative antidepressants or sedative antipsychotics use for insomnia not allowed by the protocol and unwillingness to follow the slow- taper schedule constitutes an exclusion criterion.
* No concurrent sleep medications at least 30 days prior to baseline. Exclusion criteria if the patient has withdrawal symptoms and/or sleep disturbances measured by BWSQ prior to baseline.
* Uncontrolled Severe Medical Conditions: Any condition that could interfere with study procedures, safety, or outcome measures (e.g., unstable cardiovascular, respiratory, neurological, or endocrine disorders).
* Pregnancy or breastfeeding
* Cognitive Impairments: Significant impairments that prevent the comprehension or completion of study questionnaires or procedures.
* Hypersensitivity: Known allergy or hypersensitivity to daridorexant or any of its excipients.
* Specific Sleep Disorders: Sleep apnea or hypopnea index ≥ 15 events/hour (based on American Academy of Sleep Medicine criteria) or any event associated with oxygen saturation \< 80% (as measured by polysomnography).
* Periodic limb movement index ≥ 15 events/hour (as measured by polysomnography). Restless legs syndrome, circadian rhythm sleep-wake disorders, REM behavior disorder, or narcolepsy.
* Concomitant Use with Moderate and potent CYP3A4 Inhibitors: Prohibited due to potential drug interaction (refer to protocol section 4.5 for specifics).
* Moderate and severe hepatic Impairment: Any hepatic condition deemed unsafe for daridorexant use.
* Relapse or Worsening of the Main Diagnosis: Relapse of depression whose severity precludes continued participation according to the investigator's judgment.
* Substance Use Disorder: History of substance use disorder without sustained remission. Exception: past sedative abuse may be permissible if remission criteria are clearly met, as determined by the investigator.
* Excessive Caffeine Intake: Daily consumption of \>400 mg of caffeine (e.g., \>4 standard cups of coffee).
* High-Risk Alcohol Consumption: Alcohol intake above recommended risk thresholds in accordance with the guidelines of the Spanish Ministry of Health: i.e., \>4 standard drinks/day (\>40g/d) for men, \>2 standard drinks/day (\>20g/d) for women.
