I guess every successful country has its own flavor how they managed to do it, but there are some common grounds. AI summarized it:
Health-Centered, Non-Punitive Approach: Treating addiction as a health issue rather than a criminal one, focusing on support and rehabilitation instead of punishment.
Comprehensive Harm Reduction Services: Wide availability of needle and syringe programs, supervised consumption rooms, and take-home naloxone to prevent overdoses and reduce health risks.
Medication-Assisted Treatment (MAT): Broad access to opioid substitution therapies such as methadone, buprenorphine, and in some cases heroin-assisted treatment for severe cases, improving treatment retention and health outcomes.
Low-Threshold Access to Treatment: Removing barriers so that drug users can enter treatment quickly without mandatory abstinence or heavy restrictions.
Integrated Social and Medical Support: Combining addiction treatment with social services, mental health care, housing, and counseling to address the whole person and their environment.
Community-Based and Residential Treatment Options: Offering a range of treatment modalities including therapeutic communities and residential programs that focus on recovery beyond detoxification.
Public Funding and Universal Healthcare: Ensuring treatment and harm reduction services are publicly funded and accessible to all, removing financial barriers.
Focus on Prevention and Early Intervention: Implementing school programs, community outreach, and early detection to prevent addiction and support at-risk populations.
Or there is some US-based article:
Lessons from Abroad: How Europeans have tackled opioid addiction and what the U.S. could learn from them.