Drug-Drug Interaction and Safety of AZD4041 Study (Part 1) and Efficacy, Safety, Pharmacokinetics and Pharmacodynamics of AZD4041 Study in Opioid Use Disorder (Part 2).

Inclusion Criteria: • Male participants: * with female partner(s) of childbearing potential (including breastfeeding partner) must be willing to use a reliable method of contraception throughout the study period for 30 days) after final investigational medicinal product (IMP) administration for Part 1a, and for 5 drug elimination half-lives after final IMP administration for Part 1b and Part 2. * must not donate sperm starting at screening and throughout the study period and for 30 days) after final IMP administration for Part 1a and for 5 drug elimination half-lives after final IMP administration for Part 1b and Part 2. * with pregnant partner(s) must agree to remain abstinent or use a condom for the duration of the pregnancy throughout the study period and for 5 drug elimination half-lives after final IMP administration. Part 1 * Body mass index (BMI) within 18.0 kg/m2 to 30.0 kg/m2, inclusive. * Body weight of within 50 kg to 100 kg, inclusive. * Non- or ex-smoker (an ex-smoker is defined as someone who completely stopped using nicotine products for at least 180 days prior to the first drug administration). Part 2 * BMI within the range of ≥ 18 and ≤ 35 kg/m2 at the screening visit. * Participant has a diagnosis of moderate to severe OUD according to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) using the Mini International Neuropsychiatric Interview (MINI) version 7.02. * Participant is voluntarily seeking treatment for OUD. * Participant is not currently receiving Medication for Opioid Use Disorder (MOUD), and has not received MOUD within 60 days prior to screening and is: * Willing to initiate buprenorphine therapy; * Considered to be a good candidate for buprenorphine treatment based on medical and psychosocial history; * Has a positive urine drug screen at the initial screening visit and Day -1 for opioids. These may include morphine and metabolites, diacetylmorphine (heroin), codeine, oxycodone, hydrocodone, hydromorphone, fentanyl and metabolites, propoxyphene or oxymorphone. * Female participants: * must not donate ova starting at screening and throughout the study period and 5 drug elimination half-lives after final IMP administration. * must not be planning to become pregnant during the study and at least one of the following conditions apply: * Woman of non-childbearing potential (WONCBP) and/or * Woman of childbearing potential who agrees to follow the contraceptive guidance from the time of informed consent until at least for 5 drug elimination half-lives after final IMP administration. Exclusion Criteria: * Participant has a history of attempted suicide or suicidal behavior within 12 months prior to screening or has any suicidal ideation that meets criteria at a level of 4 or 5 by using the Columbia Suicide Severity Rating Scale (C-SSRS) within 12 months prior to Screening or who is at significant risk to commit suicide, as assessed at Screening and at Day -1. * Male participants with a history of oligospermia or azoospermia or any other disorder of the reproductive system or who are undergoing treatment or evaluation for infertility. * Females who are lactating or pregnant according to the pregnancy test at Screening or prior to the first study intervention administration. * A family history of long QT syndrome. * Any abnormal or clinically significant findings in laboratory test results at Screening. * Participant has HIV per screening serology test. * Any clinically important abnormalities in rhythm, conduction, or morphology of the resting electrocardiogram (ECG) and any clinically important abnormalities in the 12-lead ECG. * History of significant allergy/ hypersensitivity to AZD4041 or to products related to AZD4041 or other study drugs (including excipients of the formulation), as well as history of severe allergy/hypersensitivity reactions (like angioedema) to any drugs. * Any vaccination (including with COVID-19 vaccine) less than 14 days prior to first study intervention administration. * Participants who have a history of exposure to psilocybin and 3,4-methylenedioxymethamphetamine (MDMA) within the last 3 months. Part 1 Only: * Past medical history of any clinically significant systemic illness including (but not necessarily limited to) cardiovascular, gastrointestinal, pulmonary, hematologic, neurological, hepatic, endocrinologic, metabolic, genito-urinary, musculoskeletal, immunologic, dermatologic, renal and/or major disease. * Maintenance therapy with any drug for long-term chronic conditions or significant history of drug dependency or alcohol abuse (\> 21 units/week or \> 3 units/day for men; \> 14 units/week or \> 2 units/day for women; intake of excessive alcohol, acute or chronic). * History of any significant psychiatric disorder according to the criteria of the Diagnostic and Statistical manual of Mental Disorders, 5th Edition (American Psychiatric Association 2013). * History of any substance use disorder (as per DSM-5 criteria). * Any clinically significant, medical/surgical procedure or trauma within the 28 days prior to the first study intervention administration. * Positive urine test result for drugs of abuse or cotinine (nicotine), at Screening or prior to the first study intervention administration * Positive screening results to hepatitis B surface antigen (HbsAg), or hepatitis C virus (HCV) tests. * Use of any prescription drugs, including hormone replacement therapy in the 28 days prior to the first study intervention administration. * Excessive intake of caffeine-containing drinks or food (e.g., coffee, tea, chocolate) as judged by an Investigator. * Presence of any tongue piercings or history of any tongue piercings in the last 90 days prior to the first study intervention administration. * Participants who have medical dietary restrictions. * Participants with a known hypersensitivity to itraconazole (Part 1a only). Part 2 Only: * Participant with clinically significant and uncontrolled cardiovascular, gastrointestinal, pulmonary, hematological, neurological, hepatic, endocrinal, metabolic, musculoskeletal, immunologic, dermatologic, renal and/or any other major disease. * Participants with a history of severe respiratory insufficiency, obstructive sleep apnea not controlled by a continuous positive airway pressure device or narcolepsy or current clinically significant infections. * Current diagnosis of chronic pain and who require treatment with opioids. * Participant has an active malignancy or a history of malignancy (except for treated non-melanoma skin cancer) within 5 years of screening. * Participant has a history of respiratory depression while on buprenorphine-based or other MOUD. * Participants with active signs or symptoms of hepatitis and requiring treatment; or known or suspected chronic liver disease, including cirrhosis or significant liver fibrosis. * Participants with current HCV infection. * Hepatitis B Virus (HBV) infection: Participants with positive hepatitis B surface antigen (HbsAg) or those with a history of Hepatitis B viral infection. * Participant has known kidney disease and a glomerular filtration rate (GFR) \< 60 mL/min/m2 at screening. * Participant has comorbid major psychiatric disorders specifically schizophrenia, bipolar disorder or severe major depressive disorder. * Moderate to severe substance use disorder on any other psychoactive substances (by DSM 5) other than opioids, caffeine or nicotine (eg, alcohol, sedatives). * If a participant is currently diagnosed with abuse of or dependence on alcohol, the participant will not be allowed to enrol in the study, unless the alcohol abuse/dependence is in full (complete, not partial), sustained (\> 1 year) remission. * Participants who need to be on prescription central nervous system (CNS) depressant medications including benzodiazepines, during the trial (other than the study interventions). * Participant has a positive urine drug screen (UDS) results for barbiturates or benzodiazepines at screening or Day -1. * Participant has a positive urine test for buprenorphine on Day -1. * Participants with a known hypersensitivity to buprenorphine, naloxone, other opioids or any components of the formulations used.