This is a really long one. Sorry about the massive wall of text but addiction by nature is complicated and always comes with a lot to unpack. It doesn't help that addiction has many causes and forms, and involves every layer of the human experience.
Drug addiction is a multi-faceted issue, and there is a lot to consider (and address). Much of which is unfortunately outside of the purview of magic.
There is a need to understand and address what enabled the addiction. Nothing happens in a vacuum. Be it through depression, peer pressure, troubled life situations, ...There are internal (psychological/emotional) and external (environmental) causes. If those are still present they will continue to feed the addiction. Basically, every addiction begins with at least one bad choice. But every choice has a cause. Until the cause is addressed, the same bad choices will be repeated over and over. And all you get is a destructive relapse cycle.
As for the chemical dependence, that is a physical process of the body. Physical addiction happens because the body develops a need to have the chemical present. Some aspect of normal function gets at least partially replaced or taken over. Usually involving the delicate chemical and hormonal balance if the brain. The drug presence works out of the system, leaving behind an imalance which creates physical symptoms. Symptoms that can range from basic discomfort, headach, and irritability (think sugar or caffeine) to hallucination, delusion, seizure, coma, heart/organ failure, and worse.
Long story short, there are no simple or swift solutions. However that does not mean magic would have no role in helping. Just that a solution will not come from a spell but rather the philosophies of exploration, Self-improvement, shadow-work, and potentially religious comfort/spiritual connection that usually runs in tandem to a magical path.
Here are the best things that you can do;
Educate yourself on what the addiction is. How strongly the drug(s) affects the body, how it (they) affect a person physically and mentally. The processes and severities of withdrawl. And medical treatment options to support breaking the dependence while safely minimizing withdrawl.
Similarly, educate yourself on the psychology and emotional processes and triggers of addiction. Learn about your family-member's specific condition and mental state, and potential family histories of issues like depression or cycles of addiction. The get consultation of ways you might help support the family member in finding and getting into programs which will help him/her get the specific help they need. Up to and including getting him/her out of environments that may be fueling the problem. Like abuse or negative peer circles.
If this family-member has a spiritual side, then it may help to support their path by finding and providing books and texts that support both that faith/spirituality and also introspection, self-help, psychological and physical care, and self-worth.
And finally, most vitally, they have to actually and genuinely want to be free of the addiction. No one can make that happen for them. And this desire needs to be more than an in-the-moment desire. It has to be a determined choice that they make, in the face of physical, mental, and social hardship that will last for months or years. Possibly as a life-long challenge.
Like I said way (way, way) back at the beginning, addiction touches every aspect of human experience. And likewise you want to approach its resolution from just as many angles. ... I just hope that this avalanche of information helps.
