Went from 150mg daily to 25mg daily methadone in 18 months + quit cigarettes 8 months ago , but health worse , ?

Multiple Causes?: You don't state what the reason is for taking methadone originally which could have some bearing on the answer. You need a comprehensive workup to see what is going on particularly from a biochemical basis including inflammatory markers such as ANA, RA, Homocysteine, CRP, Uric Acid, ESR, as well as a full metabolic panel and blood count combined with a adequate physical examination.

Cardiology?: Recommend appointment with a Cardiologist to review results & order necessary tests.