Is Methodone used for Meth-amphetimes addiction?

My relative is taking therapy. I thought he was taking the methodone at the clinic, daily, for his meth-amphenine addiction; after reading some info on web I wonder if he’s taking that treatment/therapy for a different drug problem/ or addiction. ALSO, does his eating grapefruit hurt his treatment? I meant – will it affect it? Thank you for any info/ replies. (worried sis) in USA.