Liothyronine
"After diagnosis of Grave's Disease I was given Synthroid. Took this alone for 20 years. Dosage was lowered from 0.150 to 0.125 when thought to be causing irregular heart beat. Had an "oblation" of nerves around heart area that was causing irregular beating and remained on 0.125 dosage feeling better. A new Endocrinologist had me add Liothyronine in a custom "compound" dosage of 2.5mcg and lowered Synthroid to 0.112.  One measurement was high the other low hoping to balance the two. Didn't feel a lot of improvement. Noticed I was more irritable with upset stomach. Tried it for 2 months but quit- wasn't happy with it.  I've started taking it again and have small improvements in mental clarity, regularity, but get migraines."