Hello, I have been suffering from a straining and now underactive thyroid for 20 years. Recently I moved abroad and ran out of levothyroxine. I lost 10kg in weight and felt fantastic. I got registered and and got more blood tests and it shows I need to be on it again. They tried the French drug levothyrox which had a lot of nasty side affects. This was now changed to tcaps but in both cases my weight has increased and Ive gained 3 kg in two weeks. My diet and fitness has not changed. Has anyone had anything similar. I should add that my t4 t3 was normal so it doesn't appear to be an obvious conversion level. Many Thanks.
Gaining weight on levothyroxine: Hello, I have... - Thyroid UK
Gaining weight on levothyroxine
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sheepi
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shawsAdministrator
Unfortunately, for some who're hypothyroid, levothyroxine can cause weight gain. I believe it's due to doctors not increasing dose when TSH reaches somewhere in the range when the aim is a TSH of around 1 or lower. Neither are the Free T4 and Free T3 tested and both should be in the upper part of the ranges.
I am not suggesting you change your hormone replacement because if it raised high enough you shouldn't gain weight i.e. TSH of around 1 with FT4 and FT3 in the upper part of the ranges.
Like Shaws, my first thought would be to wonder if you're on completely the wrong dose for you. Thyroid hormone is not one size fits all, its important to be on your own personal optimal dose, and to have several retests and dose adjustments when you start on hormone. Do you have any blood test results?
It's common to feel better temporarily when giving up Levothyroxine. Although usually eventually you'll slowly get worse again. It's also common to feel worse when on a low dose of thyroid hormone. It can easily take 6 months to tune up the dose. All too often people are left on these low doses long term 
