Alcohol use disorder (AUD) is a chronic relapsing disorder. Alcohol craving, a hallmark symptom of AUD that drives relapse in patients, is only insufficiently treated by existing medication. One promising new compound is Oxytocin (OXY), which showed beneficial effects on alcohol craving in preliminary clinical studies. Additionally, OXY seems to enhance effects of established medication, specifically Naltrexone (NTX), an opioid-antagonist which is approved for AUD treatment via positive synergism on neurotransmitter levels. The proposed two-armed, 1:1 randomized, double-blind, parallel group trial seeks to test the putative synergistic effects of combined intranasal OXY spray (24 IU) + oral NTX (50mg) against Placebo spray + oral NTX (50mg) on alcohol craving (primary outcome) in male and female patients with AUD that suffer from high alcohol craving, within the framework of a validated alcohol cue-and stress-exposure task (i.e. a combined Trier Stress Test and alcohol cue-exposure) that was established for screening new medications in AUD and determine their effects on craving and relapse risk. Treatment effects on additional neurobiological and biochemical markers of craving that show strong associations to individual relapse risk, will serve as secondary outcomes. Collection and analysis of follow-up data (90 days) will be performed to determine whether treatment effects relate to patient outcome.

The clinical trial period for an individual participant consists of a screening visit (visit 1), a baseline visit (visit 2) and two treatment visits (visits 3 and 4)(all within equal or less than ten days) followed by a 90 days (+/- 7 days) follow-up phase with two visits (visits 5 and 6) at day 30 (± 7 days) and day 90 (± 7 days). Visits 1 to 4 will be conducted while participants are undergoing standard in-patient treatment at the Department of Addictive Behavior and Addiction medicine at the Central Institute of Mental Health (CIMH) in Mannheim, Germany, for the medical condition under investigation.

Inclusion Criteria:

• Age between 18 and 70 years
• Patients meeting the diagnosis of an alcohol dependence according to the Internation Clasification of Diseases 10th revision (ICD10)
• Patients with at least moderate craving, i.e. either >=15 points on the Alcohol Urge Questionnaire (AUQ, range 8 to 56 points) craving scale or increase in AUQ scores by >= 50% after exposure to visual alcohol cues (i.e. minimum increase of >=4 points after cue exposure)
• Ability of the individual to understand the character and the individual consequences of the clinical trial
• Written informed consent (must be available before enrollment in the study)
• Consent to random assignment
• For women with childbearing potential, use of a highly effective birth control method until 24 hours after Visit 4 and negative pregnancy test

Exclusion Criteria:

• Subjects presenting with any of the following criteria will not be included in the clinical trial: Current psychotic or bipolar disorder or current severe depressive episode with suicidal ideations
• Current treatment with any of the following substances: Any investigational medicinal product, Opioid-containing Analgesics, Anorexics, Anticonvulsants, Opioid-containing Antidiarrheal Agents, Antineoplastics, Antipsychotics (exception: episodic use of melperone, pipamperone and quetiapine are allowed), Antidepressants (exception: allowed, when being taken in stable dose for a minimum of 14 days prior to enrolment and/or doxepin in low doses [max. 75mg daily]), Opioid-containing Cough/cold agents, systemic Steroids
• Positive drug screening (amphetamines/ecstasy, opiates, cocaine, barbiturates)
• Pregnancy, lactation or breastfeeding
• Current severe somatic comorbidities: liver cirrhosis [CHILD B or C] or impaired renal function [glomerular filtration rate (GFR)<15ml/Min] [each determined by physical examination and/or laboratory testing], severe heart insufficiency [determined by assessment of medical history], pre-existing epilepsy [determined by assessment of medical history], long-QT syndrome or cardial arrhythmia [determined by ECG]
• History of hypersensitivity to the investigational medicinal product Oxytocin (Syntocinon®) and/or Naltrexone (trade names: Adepend, Naltrexon-Hcl neuraxpharm, Naltrexonhydrochlorid Accord) or to any drug with similar chemical structure or to any excipient present in the pharmaceutical form of the investigational medicinal product Oxytocin (Syntocinon®) and/or Naltrexone
• Participation in other clinical trials or observation period of competing clinical trials, respectively.
• Acute suicidal tendency or acute endangerment of self and others

Individual de-identified data will be shared, specifically individual participant data that underlie the results of the trial (i.e. primary outcome data [AUQ scores]) will be made available with a respective data dictionary. Secondary Outcome data (e.g. fMRI data) will be made available on aggregated group level (e.g. for the purpose of meta-analyses). Related documents, specifically the study protocol, statistical analysis plan and analytic code will be shared in open-access online repositories. Aggregated data will be made available to publicly accessible repositories (Neurosynth.org), e.g. for the purpose of meta-analyses.

Data will be available upon publication of the results until 3 years after that.

Individual data will be shared with researchers who provide a methodologically sound proposal (sent to the Principal Investigator/Study Chair of the Trial).