Study of the Opioid Modulation of the Effect of Alcohol on the Dopaminergic Reward System

Inclusion Criteria: * age: 21-45 years * The subject is able to understand the nature, extent and individual consequences of the clinical trial * Maintained ability to give consent, certified by a psychiatrist (specialist) * A personally dated informed consent form signed by the test participant * No current and/or historical psychiatric disorder (secured by standardized psychiatric interview (DIAX: Composite International Diagnostic Interview)) * Non-smokers (no nicotine addiction within the last 6 months prior to sequential allocation) * OPRM1 Asp40 carrier (functional polymorphism in amino acid residue 40 of μ-opioid receptor gene (OPRM1)) (in AC for inclusion in first and third treatment arm) * Highly effective contraception method with a failure rate of \<1%: Hormonal contraceptive methods (oral: "contraceptive pill", incl. combined oral contraceptives; subcutaneous implants; injectable contraceptives); intrauterine pessary, vasectomy of the partner, tube ligation ("sterilisation") or sexual abstinence * Persons who are legally competent and mentally able to understand and follow the instructions of the study staff * MRI capability Exclusion Criteria: * hypersensitivity to the investigational product or a chemically similar substance or component of the investigational product * Participation in other clinical trials during or within 6 months prior to this clinical trial * Medical or psychological circumstances which may jeopardise the proper conduct of the clinical trial * Physical illnesses which could interfere with the planned examinations according to their type and severity, could have an influence on the parameters to be examined or could endanger the volunteer during the course of the examination * Inability to adhere to the study protocol * Limited or completely revoked legal capacity * Acute suicidal tendency or external hazard * Poor overall condition * Participation in a study using ionising radiation in the last five years. * Regular medication (e.g. MAO inhibitors) * Alcohol abuse, alcohol dependency or addiction illness / abuse of addictive substances in history * Existence of other exclusion criteria for participation in MRI examinations (non-removable metal parts in the body, left-handedness, pacemakers) * Known hypersensitivity to carbidopa or any of the other components * Relevant organic diseases: in particular: Narrow angle glaucoma, vascular diseases, central nervous neurological diseases; body weight of more than 150 kg (contraindications PET - scan) * Clinically significant deviations in clinical chemistry or haematology or clinically significant abnormalities * Melanoma-specific skin lesions or anamnesis of a previous melanoma disease * Persons who are accommodated in an establishment by court order or official order * Persons who are dependent on or have an employment relationship with the sponsor or investigator