McCall McPherson explains why standard thyroid tests (TSH and T4) can look normal while you still feel sick. Many people are poor converters of T4 into T3, the active hormone doctors rarely check. Levothyroxine alone doesn't work for them.
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So what your doctor, your clinician will tell you is I checked your thyroid labs. Your thyroid labs look great. Your your fatigue and your brain fog and your weight gain are not due to your thyroid because your thyroid numbers look awesome. However they are not checking your active hormone, your most important thyroid hormone. So the big picture on T4 based meds, and I preach this a lot is if you are on a T4 based medication it is impossible to gauge the status of your thyroid function by checking your TSH and your T4 alone. It is impossible. My practice is filled in fact a hundred percent of people at modern thyroid clinic are poor converters. Either they can't activate and convert their own endogenous T4 or crude oil hormone or they can't activate their levothyroxine. You know we have a fraction of the people on these meds but if you are out there and you are on levothyroxine and you are still having symptoms this is why have a whole YouTube dedicated to why Synthroid or levothyroxine doesn't work.