Need information a a narcotic drug called subutex or suboxonne; my 20 year old step son takes this?

Is it for pain or is it for opiate withdrawal? What is the difference between this & methadone; and if he is taking it to help get off other pain meds is he just exchanging one addiction for another

: http://alcoholdrugstreatment.info/need-information-a-a-narcotic-drug-called-subutex-or-suboxonne-my-20-year-old-step-son-takes-this