McCall McPherson explains when Cytomel (T3) makes sense: patients with enough T4 who need more active T3 to rebalance their ratio. He warns that too much T4 suppresses TSH and raises reverse T3, blocking T3 availability, and advises against compounded thyroid meds.
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I use Cytomel only when a person is producing enough T4 on their own or they have too much T4, too much inactive hormone. I use Cytomel to increase their active hormone, their T3, and to create a settling effect to lower T4 or create more balance. I don't want T4 low. I just don't want it excessive. Why? Because it can artificially suppress TSH and it can also dump to your inhibitory hormone, your reverse T3. So even if your T3 looks great, if your reverse T3 is super high, you're not absorbing the hormone that you need, your T3. I actually never advocate for compounds. In fact, I advocate for never using compounds. Why? I'll give you an analogy Dr. Alan Christensen gave me a long time ago. If you don't follow him, you should, because he's the freaking best. Love that, man. When you're baking muffins and you're baking muffins and trying to get an even amount of blueberries or chocolate chips in each one, it's kind of possible.