McCall McPherson explains why levothyroxine alone often fails: your body must convert T4 to active T3, but that conversion can stall or divert to reverse T3 instead. Doctors who only check TSH miss these problems, leaving patients symptomatic even on the right dose.
Hi, I'm McCall McPherson, co founder and PA at Modern Thyroid Clinic. And I wanted to talk to you today about why your doctor might say you don't have hypothyroidism or that your medication is fine and you still feel terrible. So to do that, I want to really dig into how your thyroid works and what information your doctor is getting that would make him or her think that. Right? So bear with me with the biochemistry. Let's start down here. So your brain sends a message to your thyroid, right, by way of a hormone called tsh, thyroid stimulating hormone. So it does just that, right? It stimulates your thyroid. This is really what regular medicine uses to diagnose and manage people's thyroid. And we're going to dig in a little deeper, and I think you'll understand why this system doesn't really work for everyone. So really, this doesn't tell me directly about output. It tells me how hard your brain is asking your thyroid to work. Right? So this stimulates your thyroid, and your thyroid secretes a hormone called Free T4. I want you to think about Free T4 like a precursor hormone, an inactive hormone. So it doesn't actually impact how you feel at all. It just is kind of like crude oil is to gasoline. So we need crude oil to make gas to make our car run, but we can't put it directly in our car, right? It has to be activated. It has to be converted to a usable form. So thyroid secretes free T4, and really one of two things happen. Well, one of three things, actually. Either your T4 is converted to what we want it to be converted to, free T3. This is our moneymaker. This is our thyroid gasoline. It's really the only thing that dictates whether you're hyper hypo or just. Right. Euthyroid. Okay? So everything relies on this T3. So either your T4 becomes T3 or it gets shunted to your body's inhibitory mechanism called reverse T3. Reverse T3 competes for production and absorption of free T3, and it's called reverse T3 because it's actually T3 in reverse. It's a mirror image, like if you hold out your hands. So let's kind of put these pieces together. Okay? If your doctor is basing your thyroid status on your tsh, what he or she is doing is assuming that your biochemistry feedback mechanism is intact. And what I mean by that is when you have enough, supposedly of both hormones, both being the keyword, it sends a message back to your brain and it says, okay, we have plenty of hormones. You can lower this person's tsh, right? We don't need to work so hard when you don't have enough of really one or more or both hormones. It sends a message back and it's like, okay, well, we really need to pick up the pace here. We need more production, so we increase the tsh. The problem with that is, especially with people on Synthroid or Levothyroxine or medications that are T4 based, tyrosine is the same. What happens with these people or even regular people who aren't on any thyroid medication that are just walking around. A lot of people have what I call a conversion problem. They have a difficult time converting their crude oil hormone, their free T4, to their gasoline hormone, their free T3. When that happens, you can have substantial crude oil or substantial precursor hormone, and it actually sends a message back to your brain that says, okay, well, we have enough hormone. We can just keep the TSH low. Well, those people go into their doctor's office and either they say, hey, I was reading online and I have like 14 of 14 hypothyroid symptoms. I think I have a thyroid problem. Then their doctor says, oh, okay, well, let's check your tsh. Their TSH looks fantastic because it's getting a feedback message from your free T4 that you have plenty of hormone. But keep in mind that the only thing that makes you feel good and healthy and vibrant is your T3. Your free T3. So you can have plenty in all the free T4 in the world, but if you can't convert it to your active form, it's not doing you any favors. The same way that we can have all the crude oil in the world, but if we can't convert it to gasoline, we're not going anywhere in our car. Right? So that's kind of one scenario. The other scenario is my own personal scenario of, well, I'm on Synthroid for three or four years and I still have all of these symptoms and I feel terrible. Why? The doctor says, oh, well, your TSH looks fine, so you don't need any more thyroid medication. Or in my case, you need less because it's too low. Well, what was happening to me and what I see every day in my clinical practice is people on Synthroid have a ton of T4 because Synthroid or Levothyroxine is T4. So of course they do. Meanwhile, they're very deficient in T3, and. And often their reverse T3 is elevated. All of this combined just sends a message back to the brain and says we don't need to work as hard. Lower the TSH and people are left feeling miserable, and they're left having their doctors tell them that their labs are fine, that this free T3 and free T4 reverse T3. That's silly business. Who needs that anyway? When really it's impossible to know someone's thyroid status unless you have this information? Because if I had to prioritize importance, TSH would be on the lower end of the spectrum. So that's a little bit of information. If you want more information, and you really want to understand how your thyroid works and what labs are good and how they interact together, check out our course below at the link. Thanks.
Is It ADHD or Your Hormones? The Thyroid & Perimenopause Connection with Dr. Jolene Brighten
