How do you help somebody addicted to marigauna?

Although marijuana addiction can cause problems, it is not a problem in and of itself.

Your best bet is to gain stronger influence over the person you are trying to "help" and then use that influence to show them how quiting marijuana will improve their quality of life.

You also might try and introduce them to cool people, or attractive people of the opposite sex, that do not enjoy or approve of marijuana. If the person becomes friends with these people, then there will be more pressure on him/her to quit marijuana, in order to fit in with these people.

Ultimately, your options will be limited by your relationship with this person.