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).

This study will be conducted in 2 sequential parts. Part 1 (Phase I) will include healthy participants and will be conducted as two separate parts. Part 1a (DDI cohort) is an open-label, fixed sequence study part which will comprise of: * A Screening Period from Day -28 to Day -3. * Three treatment periods: * Period 1 (Day -2 to Day 5): Participants will be admitted to the clinical unit on Day -2 and will receive a single oral dose of AZD4041 on Day 1. There will be a 5-day washout period. * Period 2 (Day 6 to Day 8): Participants will receive itraconazole for 3 days from Day 6 through Day 8. * Period 3 (Day 9 to Day 22): On Day 9, participants will receive single oral dose of AZD4041 co-administered with itraconazole. Itraconazole alone will be administered from Day 10 to Day 21. * A Follow-up Visit: Participants will return to the clinical unit at least 7 days and no later than 14 days after discharge. Based on the results from Part 1a, an optional part of the study (Part 1b) may be conducted to assess the safety tolerability and PK of AZD4041 after a single oral dose. Part 1b (Single Dose Cohort) will be a randomized, placebo-controlled, double-blind (participant and investigator blinded) study part conducted in healthy participants. This study part will comprise of the following: * A Screening Period from Day -28 to Day -3. * A Treatment Period: Participants will be admitted to the clinical unit on Day -2 and will remain in the unit until Day 4, when they will be discharged after completion of all assessments. * A Follow-up Visit: Participant will return to the clinical unit at least 12 days and no greater than 16 days after the last AZD4041 PK sample. The results from Part 1 will determine the AZD4041 dose selection and safety margin to be used in Part 2. Part 2 (Phase IIa) will be a randomized, placebo-controlled, double-blind study. Participants will be randomized to 1 of 2 treatment arms, AZD4041 or placebo, in a 1:1 ratio. Part 2 will consist of: * A Screening Period from Day -21 to Day -2. * A Treatment Period: Participants will be admitted to the clinical unit on Day -1 and will receive either AZD4041 or placebo with hydromorphone (as a replacement opioid) on Days 1, 2 and 3, and buprenorphine/buprenorphine + naloxone (as a standard of care for their opioid withdrawal) on Days 4, 5, 6 and 7. Participants who complete the treatment period will have continued access to Suboxone (buprenorphine + naloxone) during their Follow-up period, which will be supplied to participants at discharge (Day 7). * A Follow-up Visit: Participant will return to the clinical unit at least 7 days and no greater than 9 days after the last AZD4041 dose.