Is it possible to mix your methadone with marijuana? Is it?

i just heard some people talking about how they crushed up a LITTLE bit of methadone and sprinkled it on their marijuana, and it worked good. Could people actually do that? is it called Lacing weed? My sister think it would work good because she already does both, methadone for pain, she broke her back and ribs. pain management?

: http://alcoholdrugstreatment.info/is-it-possible-to-mix-your-methadone-with-marijuana-is-it