Thousands and thousands. There is an osteoporosis risk with over-suppression of TSH, but that has made doctors too conservative. Apparently people who were using thyroid for weight loss had spectacular osteoporosis and it really scared doctors. Even worse, the American Endocrinology Society promotes treatment with only T4 for almost everyone because of the steadier blood levels of hormone and some side effects of T3 treatment on heart. You have to fight tooth and nail to get onto T3 or natural thyroid, and to get enough to feel well. Maybe we are risking osteoporosis and heart disease, but I can't live my life hypothyroid to "save" my body for the future. That's insane!
I got good news yesterday too. My cholesterol has dropped 35 points since I started the 25 mcg of T3. Apparently my high-ish cholesterol was yet another symptom of hypothyroidsm and I needed some T3 to get down to normal cholesterol.
You should read what my doc gave me yesterday (written by Dr. John C. Lowe) about why docs ASSUME TSH-suppressant thyroid supplement doses cause osteoporosis and heart problems. The study on TSH-suppression and heart problems was done on elderly, bed-ridden patients (who were already heart challenged). There was no control study done on healthy heart patients to support the heart disease conclusion.
I would like to read that study about people using thyroid for weight loss and getting osteoporosis. So many irrational conclusions have been made from studies about thyroid treatment. Doctors tend to only read the 'headlines' of studies and not read all the information and make their own conclusions.
Fortunately I didn't have to fight my doc to get on T3. I merely asked her to do a free T3 test after I'd taken T4 supplement for months and still had hypo symptoms. My low free T3 results convinced her that I don't easily convert T3 to T4. I started at 5 mcg 2x daily. I now take between 25-30mcg daily to prevent hypo symptoms. However my 'doc' is a naturopath, not an endocrinologist. I've noticed that naturopaths tend to respect their patients' reported symptoms more than test results.