My wife's breast milk production has greatly reduced after her levoxyl (thyroxine) been readjusted to 50 from 75. is it possible coz nothing else has changed.?

Unlikely: Although Levoxyl (thyroxine) can have endocrine and metabolic adverse effects, such as menstrual irregularities, i doubt that your wife's diminished breast milk production is related. As an aside, although Levoxyl (thyroxine) enters breast milk, adverse events to infant or mother during breast feeding have not been reported. I am not sure of the cause of your wife's decreased milk production.