Significant weight loss does not usually accompany hypothyroidism. He should have had thyroid antibodies done to confirm that he has an autoimmune thyroid disease. Assuming so, then he ought to be screened for celiac disease (transglutaminase antibodies), Addison's disease (21-hydroxylase antibodies) atrophc gastritis (parietal cell antibodies, IgA deficiency and diabetes (GAD and IA-2 antibodies) since he would have some increased risk of these additional problems. Should he have such done if not already done and a positive be found, then please send back the abnormal result and I will explain what needs to be done further. I suppose that he is not taking pills for attention deficit disorder as these can induce weight loss.
Kind regards,
Noel Maclaren MD