40 mg. is quite a lot, but from what I've read, a lot of doctors tend to wait to see if a patient develops symptoms of liver problems instead of ordering tests. Dark urine, yellowing skin/ eyes, fever, sore throat are symptoms. Knowing my tendency to be sensitive to medication, I asked my endo. to order the liver panel when I was on methimazole (only 5 mg.). I had no symptoms and had only been on it for 7 weeks. He said he had only seen liver issues once or twice in his 12 years of practice. Yet, there I was with liver enzymes 8 times the normal range 7 weeks later! I stopped the meds. that night obviously. 3 days later my enzymes were retested and they were coming down & eventually, they were totally normal once again. My baseline was normal before methimazole, so it wasn't from being hyper at all. I would get the lab done if you can- just for your peace of mind anyway. You're probably fine as liver issues are not common, but why wonder about it when you can know with a blood test? Especially at a high dose, I would do it.
Homeschooling mom to 4 wonderful boys!
Diagnosed with Graves Disease after my 4th baby- March 2012
Started on 5 mg. of methimazole daily for 7 weeks
Euthyroid at the end of those 7 weeks, but had to stop methimazole as liver enzymes were 8 times normal range.
Total Thyroidectomy- 6/15/12
Started Synthroid (brand name) 100 mcg. 2nd day after surgery for 6 weeks (TSH: 6.35 & free T4 in upper range and T3 just under mid- range).
Upped Synthroid to 112 mcg. 7/27/12
Euthyroid as of 8/10/12 on 112 mcg. Synthroid (TSH .79 and free T4 in upper range).