The current first-line treatment for opioid use disorder (OUD) in Canada is buprenorphine/naloxone (bup/nx). The standard induction method of bup/nx requires patients to be abstinent from opioids and thereby experience withdrawal symptoms prior to induction, which can be a major barrier in starting treatment. Rapid micro-induction (also known as micro-dosing, low-dose induction) involves the administration of small, frequent does of bup/nx and removes the need for a period of withdrawal prior to the start of treatment. This study aims to compare the effectiveness and safety of rapid micro-induction versus standard induction of bup/nx in patients with OUD.

This is a randomized, controlled, open-label superiority trial involving 50 individuals with OUD. Participants will be randomized into two arms: rapid micro-induction and standard induction (based on the American Society of Addiction Medicine Practice Guidelines and product monograph) of bup/nx.

Inclusion Criteria:

1. Opioid Use Disorder (OUD) as defined by the Diagnostic and Statistical Manual of Mental Disorders-5 diagnostic criteria;
2. Individuals seeking Opioid Agonist Treatment (OAT);
3. Be 19 years of age or older;
4. Be willing and able to adhere to the study protocol and follow-up schedule;
5. Be able to provide written informed consent to participate in the clinical trial.
6. If female and of childbearing potential, agree to use an effective method of birth control approved by the study investigators throughout the study.

Exclusion Criteria:

1. Diagnosis of severe medical or psychiatric conditions contraindicated for buprenorphine/naloxone or hydromorphone treatment;
2. Anticipated deterioration of health due to discontinuation of medications that are contraindicated with buprenorphine/naloxone and/or hydromorphone;
3. Positive pregnancy test for women of childbearing potential;
4. Methadone use in the past 5 days;
5. Buprenorphine use in the past 5 days;
6. Known allergy or sensitivity to buprenorphine/naloxone and/or hydromorphone;
7. Anticipation that the patient may need to initiate pharmacological treatment during the trial that is deemed unsafe by the study physician or could prevent study completion;
8. Unwilling or unable to use an effective method of birth control approved by the study investigators throughout the study.

There is no plan to make individual participant data available to other researchers.