I travelled alot from Houston to Sweden and take 9 meds, three that are scheduled, restoril,klonopin and adderall/conerta and at one time hydrocodone
I never had a problem but was always sure that my meds were in a bottle with
pharmacy label on them (with my name of course)
My stimulants/amphetamine is the same class as the methadone so I would say, based on my experience, you will be fine.
You could always call the airline and ask if there is a special procedure to travel with narcotics.