
What Causes Rapid Weight Gain While On Synthroid?

ps - I had Graves Disease 35 years ago, treated with Radioactive Iodine. Currently on Synthroid .125 daily.
Have gained over thirty pounds in past six months with no reason.
Weight gain
Detailed Answer:
Sorry to learn about your bothersome symptoms.
That is indeed a significant amount of weight gain.
Regulating the thyroid well is important. So checking the thyroid blood tests is relevant.
Testing for Cushing's disease as you have mentioned is also important. There is another rare condition called Acromegaly which can also cause weight gain. A blood test called IGF1 (Insulin like Growth Factor 1) is a good way to screen for this possibility.
When I see someone like you in my practice, I typically order the following blood tests in addition to a detailed physical examination:
CBC (Complete Blood Count, also known as Hemogram; includes Hemoglobin, WBC and Platelet counts)
Electrolytes (Sodium and Potassium in particular)
HbA1c (Glycosylated Hemoglobin = your last 3 months' glucose average). Also known by other names such as GlycoHemoglobin or Glycated Hemoglobin or A1c
Liver function tests (SGOT , SGPT, Albumin, Bilirubin, Alkaline Phosphatase)
Kidney function tests (BUN, Creatinine)
TSH (checks your thyroid)
Free T4 (this too checks your thyroid)
25 hydroxy Vitamin D levels (ideal range 40 to 60 ng/ml = 100 to 150 nmol/liter)
IGF1 (Insulin like Growth Factor 1)
None of these tests require any fasting and can be done at any time of the day

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