And you can refer to this review as a reality check against all the non-evidence based prescribing and thyroid quackery out there.
It is available as free full text but here are a few take home points:
Start full dose replacement in younger and otherwise well patients.
Start low and go slow in older folks.
Start even lower in those with known CAD and those who might be suspected to have silent CAD based on risk factors, including the severity of the hypothyroidism itself.
Although subclinical hypothyroidism has an association with some adverse cardiovascular outcomes, whether treatment of same is beneficial is controversial. Treatment can often be withheld provided there is careful follow up, as many patients spontaneously revert to normal laboratory status.
Although the use of triiodothyronine and dessicated pig thyroid extract are employed by many practitioners they are unsupported by high level evidence. Further research is needed to define whether there are populations that will benefit from the adjunctive use of triiodothyronine.
This is all pretty much in line with an older review I blogged several years ago.