I don't think that magick can *make* someone do anything that they do not want to do. Also, it is not in good practice to cast a spell or ritual on/for someone without their knowledge or consent.
After getting their permission, you can formulate your own spell or ritual to cast to help or sway this person. Much research should be done regarding what types of things can help in this kind of spell. There are also a few ways you can approach this situation. You could view it as a problem that needs cleansed or banished, a habbit that needs bound, an illness that needs healing, a psychic energy imbalance that needs corrected, and for each viewpoint there is a different means for fixing. An amethyst crystal can help to heal addiction, and malachite can be used to remove any subconscious blocks that may be preventing this person from overcoming their addiction. Quartz Crystal can be used for healing or to amplify the powers of other stones used. You could use a white candle for cleansing and purification, or a green one for healing, or a black on for banishing any negative energies that may be at play. I am more of a hands on person, and find that my spells are better when I create something like a charm and give it to the person to carry.
You could cast the spell without this person, or perform a ritual with their active participation. You could cast a single spell, or utilize multiple days to build the energies that are working in your favor. I personally might think that a few smaller spells throughout the week, each approaching it from a different angle, would do best. Combined with a generalized healing ritual during the upcoming Full Moon to really nail it home. Though, most do not recommend working on one single spell for more than a day, and even recommend not thinking about the spell after it has been cast. If you believe that thinking about it or casting multiple spells for the same thing might alter the effects, I would suggest researching and constructing your own personalized ritual and performing it during the Super Blood Wolf moon next Sunday. Im not exactly sure how the moon will effect magicks, but I expect it to help amplify the energies and outcomes.
Leaving the magickal perspectives aside, you should recognise that addiction in a serious ailment. It is great for you to want to be there for this person and to help them overcome it. Battling addiction tends to be an uphill battle that addicts need plenty of support and resources for. Even the best can fall backwards sometimes and need picked up again. This person can't do it alone, and will need everyone that can be there for support. Although a spell may be a good approach, addiction really needs to be combatted on the front of the individual battling it. It will take commitment and perserverence and maybe a rehab or two, but it also has to be a choice on the behalf of the addict. Im not saying that they choose to be addicted, but some may choose to believe that it is no big deal and that they are just fine. Sometimes they need people to show them that it is a problem, but sometimes they hate that. A lot of times the person needs to stop hanging out with their old "crew" and find new healthier friends to prevent a relapse. I hope you and your family and this persons family can ban together and be the help and support that this person needs. I wish you the best and hope that this person can find a way out.