Monitor dosage of hormone

DEAR DOCTOR K: I have hypothyroidism and take synthetic thyroid hormone. Is it OK to switch brands or switch to a generic?

DEAR READER: It’s OK to switch, so long as your doctor monitors your thyroid blood tests.

Hypothyroidism occurs when the thyroid gland is not making enough thyroid hormone. Two blood tests are used most often to diagnose hypothyroidism; they measure the levels of the T4 and thyroid-stimulating hormone (TSH). TSH is a brain hormone. When the brain senses your T4 levels are low, it makes more TSH. The TSH then signals the thyroid to make more T4.

So, paradoxically, when your thyroid gland starts to not make enough T4, your T4 level is low but your TSH level is high. These tests help diagnose hypothyroidism, and enable your doctor to determine if your treatment dose is correct.

There are many brands of synthetic T4, and each is as good as the next. However, problems can occur when you switch brands. Small differences between brands can significantly impact how much T4 your body absorbs. Even slight changes in amounts of T4 absorbed may affect your overall health.

If you must switch – if your health plan changes its list of approved drugs, or if another brand is cheaper – tell your doctor. He or she should measure your TSH level after you start the new brand and make necessary adjustments to your dosage.

I also wouldn’t recommend taking a generic version of synthetic T4. You’re not guaranteed to receive the same generic version every time you refill your prescription. This inconsistency may throw off your thyroid hormone levels. What’s more, the FDA allows a certain degree of difference between a generic and its brand-name equivalent. This slight difference can have a significant impact on thyroid hormone levels.