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Dr Adi
Dr Adi, Professor
Category: Endocrinology
Satisfied Customers: 440
Experience:  Director of the Pediatric Diabetes Clinics at UCSF.
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I have been on synthroid 10 years, however in all that time,

Customer Question

I have been on synthroid for over 10 years for hypothyroidism, however in all that time, they still have not regulated my dosage. In the past year and a half, my dosage has went from 175 mcg to 112 mcg. My bloodwork always shows low TSH and normal T4 and T3. My question is, why does my TSH keep getting lower with the decrease in dosage? The T4 stays relatively the same. My TSH at 175 mcg was .03 uIU/ml, .023 at 130 mcg; and is .01 at 112 mcg. My T4 stays at 1.40 to 1.41 nc/gl.
Submitted: 1 year ago.
Category: Endocrinology
Expert:  Dr Adi replied 1 year ago.

Hi there,

Good question. The original dose of 175 was probably too much because your TSH was too low (too much thyroid suppresses TSH). If that is the case, decreasing the dose may not cause an increase in TSH until it reaches a point when the thyroid dose and level is less than optimal, then the TSH can begin to rise.

Having had suppressed TSH for long time, it takes a long time to get it to "wake up" and rise, often months, sometimes years. In addition, your T4 does not seem to change with changing the dose, likely due to a concomitant change in your thyroid requirement; the older you get the less you need.

Most endocrinologist will aim for a TSH of 1-2, AND a clinically feeling well patient with no symptoms of hypothyroidism nor hyperthyroidism. There is a tendency for people to over-treat because of a common complaint of "fatigue, low energy, weight gain, etc." which may not be always related to thyroid levels.

Long answer, but I hope I addressed your question. Thanks.