T4 converts to T3 which is the active form that your body uses. Many people have conversion problems T4 to T3. T4 is more old school as more docs are learning that T3 daily is much more effective since it's easier to control levels. Most doctors don't like the thyroid meds that have both t3/t4 for this reason as what's the point? Just more hardly to stabilize and harder to make custom dosages since the t3/t4 meds in 1 pill have predetermined dosages.
I try not to be too sarcastic...
But thank you for telling me how t4 and t3 work.
I have Hypothyroidism and Hashimoto's Thyroiditis.
I have a Endocrinologist and a family practitioner who disagree with you.
Also, every new study has determined combination therapy's to be far more effective than T3 by itself..
Hence why dessicated thyroid is so common.
T4 is not JUST used for T3 conversion
I could also list off the studies where T4 is used as opposed to T3 (Growth hormone deficiency OR T4 deficiency caused by HRT)
This is not just a cutting drug.... T4 is a multifaceted drug