The problem is twofold. Doctors don't seem to recognize that Thyroid med is not directly additive to prior levels. When you start taking levothyroxine or other T4 med, your TSH (thyroid stimulating hormone) goes down, resulting in less stimulation of the thyroid gland and less output of natural thyroid hormone. The net effect is basically no change in your important thyroid levels: Free T4 and Free T3, until your med dosage is adequate to essentially suppress TSH level. Then further increases in dosage allow your your Free T4 and Free T3 levels to rise as needed to relieve symptoms.
Doctors will tell you that T4 always converts to T3 as needed by the body. This has been scientifically proved wrong. There are a number of variables that affect conversion, including TSH. Thus when taking T4 med, like Levo, the reduced level of TSH typically causes reduced conversion of T4 to T3. Even by taking the med in a single dose, as compared to a continuous low flow in the natural state, it spikes FT4 for a short time and suppresses TSH for most of the day., making TSH an inaccurate diagnostic during treatment.
Hypothyroidism is best defined as "inadequate T3 effect in tissue throughout the body, due to inadequate supply of, or response to, the thyroid hormones". For adequate treatment, your med dosage should be increased to raise both FT4 and FT3 as needed to relieve hypo symptoms. Med dosage should not be adjusted based on TSH. That does not work.
In addition there are other variables that are important for you. Vitamin D is important for its effect on the body's response to thyroid hormone. D should be at least 50 ng/ml, B12 is important in preventing fatigue and should be in the upper part of its range. Ferritin is very important and should be at least 100.
If you have been tested for Free T4, Free T3, Vitamin D, B12 and ferritin, please post results and the
ranges shown on the lab report. If not, you need to get those done first thing.
Most important, you need a good thyroid doctor who understands all this and is willing to treat clinically, for symptom, rather than based on TSH. Do you think your doctor will do that?
If you want to confirm all I have said here, I suggest you go to the following link and read my paper.
Don't know why they should have different effects since they are both T4. Did you change anything else during the time you switched that could have affected absorption or conversion to T3? What were your FT4 and FT3 levels before and after the switch to Synthroid?
Hello, I hope you switched to Synthroid... I was switched to Levothyroxine, the generic form of Synthroid, and it was the worst experience. My mom had a similar bad experience with Levo. I got her to switch to Synthroid and all of her horrible side effects were gone. I've been on Synthroid for over 15 years, works well.