depends on the dosage in my experience.I use Tiromel, from BG and I've used other sources also. I don't "feel" Tiromel at all, but I think it works. Not "feeling" T3 seems to be a common debate. Here, perhaps me not "feeling" Tiromel could mean it is underdosed or even fake, but not everyone feels T3. I know that people love the Mexican T3, which is a brand named Cytomel, and they claim it raises their heart rate and acts like a stimulant, and so without testing it, you'd make the assumption that it's real or what T3 "should" feel like. I've never tried it though.
Tiromel has less excipients and is a cleaner product than Cytomel, so the difference in feeling may be due to the different excipients.
There's such a wide range of individual feelings when taking T3. I am one of those people that doesn't feel T3, but I am pretty certain it is working.
from 50µg on, it will def increase hr and flatten you out