The answer depends on how severe the addiction is. If the person is severely addicted, meaning that they are using daily, unable to live any semblance of a normal life, and are nearly always under the influence, then inpatient treatment is usually best, which may include a medically-guided detoxification period.
If a person struggles with addiction and is an appropriate candidate for outpatient therapy, then there are many therapies that can be helpful. Common therapies include Motivational Interviewing, Cognitive Behavioral Therapy (CBT), Medication Assisted Therapy (MAT), and Trauma-focused therapies.
These therapies can be effective as long as there is also a behavioral plan to address decreasing use. Clients can address underlying emotional or mental health issues, but only if they are making significant progress toward sobriety. Relapses happen, but therapy cannot work if the client is using all the time, or are high during sessions.