Rich has been taking Synthroid or levothyroxine for many years.
When Rich came to my office for continuing management 10 years after his bypass surgery, I checked his thyroid panel:
TSH 7.44 uIU/L
Free T4 1.88 ng/dl (Ref range 0.80-1.90 ng/dl)
Free T3 2.0 pg/ml (Ref range 2.3-4.2 pg/ml)
Rich's thyroid hormone distortions--high TSH, low T3--are sufficient to account for a tripling of heart attack risk long-term.
As Richs' thyroid was being managed by his primary care physician, I notified this doctor of Rich's panel. He therefore increased Rich's levothyroxine from 75 mcg per day to 100 mcg per day. Another thyroid panel several months later showed:
TSH 0.98 uIU/L
Free T4 2.38 ng/dl
Free T3 2.0 pg/ml
As you would expect, increasing the intake of the T4 hormone (levothyroxine) increased free T4 and suppressed TSH.
But what about T3? It's unchanged.
Indeed, Rich says that he feels no better and, in fact, wakes up in the morning foggy and requires a nap in the afternoon.
In my experience, the majority (approximately 70%, but not 100%) experience subjective improvement when T3 is added in some form and the free T3 level is increased. While the data (summarized here) are conflicted on whether there is objective benefit to T3 management and supplementation, there seems to be a poorly-quantified subjective improvement.
Rich's increased levothyroxine dose decreased (calculated) LDL cholesterol by 10 mg/dl. Based on my experience, I'll bet that his lipid panel would likely be further improved with T3 correction.
What I find incredible is the absolutely rabid resistance waged by primary care physicians and endocrinologists against this notion of T3, mostly due to fears of the remote likelihood of inducing atrial fibrillation and osteoporosis, while they are ready to prescribe lifelong statin drugs without a moment's hesitation.