What Are the Downsides to Using Methadone for Addiction Treatment?

I have a friend who has finally decided to get herself treated for her heroin addiction. I’ve heard a lot of good things about buprenorphine as a detox option, but I know that a lot of people are still banking on methadone as a good way of detoxing. I just want to know the disadvantages of using methadone so that I can warn my friend as well as help her in making a decision.