We do know that confrontation or strong criticism is usually not helpful in getting people living with bipolar the help they need. Dramatic “interventions” are only effective on daytime TV talk shows. Research shows that confrontation or emotion-charged criticism increase risk of decompensation in young people with bipolar disorder.
I’d recommend some specific things you might try:
First, express your concerns about marijuana use. You can try saying something like, “I am concerned that you are not getting out much or enjoying yourself. And I worry that using marijuana contributes to that. Do you think that using marijuana is holding you back from doing things you would like?”
Your goal is to raise the question rather than insist that you know the answer. In the end, cutting down on marijuana is the only way to answer that question.
Second, express your concerns about the medication plan. You can try saying something like, “I am concerned this medication is not helping you as much as it should. Could I come along with you next time you see your doctor to let him/her know what I see?”
Third, try to identify some specific goals you can support. You can try saying something like, “Are there specific things you and your therapist are working on—things you want to try doing or doing more often? How can I help you to get going on those things?”