This is where I am right now. Initially the doctor started me on 50 mcg of synthetic T4 (Euthyrox), however after almost 4 months of feeling not even a bit better, I researched about the best treatments for hypothyroidism, and one other option that I saw many people were happy with was using only synthetic T3, the active hormone that the body actually needs. This is because for many people the conversion from T4 to T3 doesn't happen or it's very slow, so taking T3 directly bypasses the entire conversion issue.
Some of the brands synthetic T3 is known over the world are: Cytomel. Cynomel, Linomel, Tiromel, and also the generic T3 (it's the one I'm also taking, shown in the picture here).
Personally for me taking T3 helped a lot. I don't say I'm 100% well, I still have times of slight brain fog (watching a movie and not remembering the name of a well known actor is no fun!), I still have now and then various symptoms, however I do want to stay at the lowest safe level of T3 that I can while feeling as best as I can.
Taking T3 only has its dangers as well. It's very easy to over-medicate (yep, been through it and it was not fun). Some people even take it to lose weight or for body building - which I find wrong. They take a huge amount of pills, while for real patients who have hypothyroidism problems the dosage is usually very small.
The other problem with taking T3 only is that the blood results from now on will not be accurate anymore - if at all, so you won't be able to rely on them going forward. You will really have to rely on your own signs and symptoms of hypothyroidism to know how you're doing on this pill.
In fact, at this point using the TSH blood tests as measurements can be quite dangerous for the person because the blood tests can not show any activity that happens at the cellular level, where the T3 is in fact needed.
Another problem is the fact that taking T3 is not all that easy. Because of its short action, it needs to be taken several times (at least twice) a day. Taking synthetic T4 is very easy: you only take a pill when you wake up. Taking T3 can be complicated by the fact that people might forget to take a pill now and then. Not good.
So before starting on T3 only, make sure that you've really tried for at few months at least to take a combination of T4 and T3, because that is much, much easier to manage overall.
Image source: taken from my own box of T3 thyroid medication