Decreased muscle mass as a side affect of levothyroxine

I have been on levothyroxine for decades and it hasn't affected my muscles or strength at all. I hate to say this, but could it just be you're getting older?

Hi. I have been on levo since 1995 and no issues with muscle mass. I walk a few miles a day and also lift light weights. I am 72.

Should not be taken with other medications
Levothyroxine should not be taken with other medications. Other medications can stop levothyroxine from working. It is recommended to separate the administration of these medicines from levothyroxine by 4 hours. Taking other medications with levothyroxine may lead to being "under-replaced" or "over-replaced". Certain other medicines may also increase or decrease the effects of levothyroxine. It is best to take levothyroxine alone, on an empty stomach, and with a full glass of water for best absorption.
Drugs.com
+4 Just in case, I would match your Levothyroxine with other meds you take just to be sure.

Thank you. That is what I do. I do not take any other meds, vitamins or supplements until 4 hours after taking Levothyroxine.

Thank you. I walk and work out 3 times a week. I am physically active otherwise.

I've been on levothyroxine for 30 years. I practice yoga and have never lost muscle mass. In my 60's I have seen changes related to age. When I started dealing with back spasms a year ago, one doctor joked, "Maybe you are just really out of shape," Not helpful. With chronic autoimmune illness I have found that I can take what is helpful from doctors and ignore the rest.
Also, I found the best treatment for Hashimoto's thyroiditis was to see an Endocrinologist. Most complete exams and prescribing levothyroxine.
I hope you find an endocrinologist. Take care!