I have noticed a distinct difference between how I feel when on FDA approved T3 and T4 versus compounded thyroid hormones. Lab results also show that my numbers are more regulated and don't seem to fluctuate so much on compounded thyroid medications which is probably why I feel better. Another benefit to compounding has been to decrease or eliminate fillers that I tend to be sensitive to. Lastly and more of a convenience factor is that I am able to get both T3 and T4 compounded together into one capsule which makes traveling with less bottles helpful.