Opiates will bind you up! Ask your Doc for "Linzess" or "Amitiza"....they aren't laxatives but you take them daily so you can go. I'm on opiates 10 yrs. now for a fractured hip and I use those meds. Remember, I'm NOT a doctor; this is just MY experience. Use Miralax, too. ;-)
Methadone is very constipating. I know a person who found probiotics helped some. In addition to that, you can try various laxatives. I've heard Vitamin C helps, but I think that's because it counteracts the methadone; your doctor may recommend against Vitamin C.
It's an endless problem. The only real solution is slowly taper off the methadone -- but only when you are ready! (We taper off SLOWLY so the brain doesn't realize what we are doing.)
Try some stool softeners. They work pretty well. Good luck let us know how you do.
I used suppositories. Worked fine for almost 7 years. Have a plan to taper off Methadone. Slow and steady. Meet with your doctor ahead of time to get the meds figured out before you can't think. The withdrawals are worse than almost 400mg oxy/day, Suboxine coming off 24mg/day, H/brown/heroin, BY FAR!! Almost 6 weeks before I could WALK to the kitchen... Suboxine took 3 months to be good. This M can take 6 months.. Gets in your BONES!!!!