I started taking Levothyroxine in Dec. 2013 (25 MCG). In Feb. 2014 it was increased to 50 MCG. About a week after starting at the higher dose I started experiencing severe leg cramps when I retired for the night. They are so bad that I can not lay on either side and am constantly jumping out of bed because of the cramping. Prior to taking this medication I had no problem with leg cramps. I stopped taking the medication 3 days ago and find the cramping is subsiding considerably.
Hi I am Chat Doctor. .  In my opinion yes I think it's the cause of your severe leg cramps but indirectly as a lot of studies say that it decreases the bone density and thus alters serum calcium and other minerals .  For now I suggest some lab investigation to diagnose mineral level in blood for proper evaluation and management, However, estrogen use appeared to negate the adverse effects of thyroid hormone on bone mineral density. I think you may need to decrease dosing or ask your endocrinologist for the best alternative for your case that suits your body requirements.  Please click THANK YOU and consider a 5-star rating with some positive feedback if the information was helpful. Hope the above information helps you, Any further clarifications feel free to ask.