If he's taking 1200 mgs of magnesium twice a day, that's quite a lot - i wouldn't increase it. Chelated forms like magnesium glycinate are easier on the bowels.
Pdoc sounds like a dolt - can you talk to his primary care doctor and show him the papers I linked? Maybe HE could be persuaded to talk to H and recommend a change.
Who picks up his prescriptions? If it's you, couldn't you just "forget" to pick up his Mirapex for a while? (I wouldn't stop the Effexor suddenly, even though I agree with you, it may be contributing to the problem).
With his family history, thyroid disease is definitely a possibility. Make sure his multivitamin has some iodine in it, and consider adding 200 mcg selenium, which has been shown to reduce thyroid antibodies and is a cofactor in converting T4 to T3.
