Can Methadone Taken For Several Years Cause Constipation And Other Digestive Changes?

my son has been on methadone for 12+ yrs. he is now 34 yrs old, for the last 8 months at least he has had problems with his methadone not working, does have gi problems - mostly constipation - untreated except diet changes, but he was also bitten by tick 17 yrs ago - lyme tests negative (not reliable) he is experiencing bad withdrawals and pain even though on 160 ml methadone - dose level same for some time now - experiences dramatic flucuations in effects of methadone and he has been clean and sober for 5+ years, has chronic inflammation from lyme , diet helps inflammation (no sugar, --), and is anemmic for long time, but his absorbtion maybe?? not absorbing methadone?,