Heart rate falling as I increase T3: Hi I have... - Thyroid UK

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Heart rate falling as I increase T3


Hi I have been trying to increase my T3 trying to work out what my optimal dose it. I currently take 75mcg per day. Have had undiagnosed hypo for 20+ years so I have a long history to work through.

When I increased gradually to near 100mcg a day rather than my heart rate increasing, which I was expecting as I get near the top of my tolerance, it actually decreased to around 57/58 bpm. Has anyone else had this experience and do you know what it means?

thanks very much


8 Replies

Hi, what was your HR before you started T3. My resting HR has always been around 60, I take 40 mcg T3 split into 3 doses. HR rate does vary from lowest 52 to 66 highest. Values taken from Apple 4 watch. I certainly don’t get spikes in resting HR after I take T3.

Sertiko in reply to Airmed

Hi Airmed thanks very much for replying. Before I started taking any T3 my HR was around 55 bpm. When I started it gently trended upwards to between 59-62 bpm. I thought that increasing the dose from 75mcg to 100mcg would cause my heart rate to increase as this is one of the signs of hyper. But instead it went down to 57bpm. I think I read somewhere that this could be a sign of adrenal insufficiency so wanted to know if anyone else had a similar experience.

Best wishes


Airmed in reply to Sertiko

Sorry no idea about adrenal stuff. I do know that when I increased my dose (due to fact taking well expired T3 and wondered about efficacy) to 50 mcg my hair started to fall out. That was a problem for me when I was hyper so went back to 40 and all ok now. No change in HR though.

Sertiko in reply to Airmed

Ok thanks for replying to me and hope you continue to stay well. This is a battle! : )

Sertiko just thought I would let you know that when I raised my T3 by .25 mcg from .25 T3and 75 mcg T4, my actual FT3 went down a bit. I just felt that my T4 and T3needed balancing a bit better though and have still not achieved this.

Thanks J Bee I appreciate you replying. This is an ongoing struggle so I hope you stay well x

Make a note of the time of day you take your pulse (or HR). It should be a minimum first thing in the morning - before you do anything, including going to the toilet. Measure your pulse the minute you awake. As you go about your usual day your pulse will increase, for me it increases by about 15bpm (from 60 resting to ~75 walking around). So, what I am trying to say is that 2 or 3 points either way is within a margin of error and you should not draw any conclusions from that. As a matter of fact, if you sit quietly and take your pulse, (and write it down) and then take it again 3 or 4 times you will see it drop as you move into a resting state.

I am fascinated though by the fact that your pulse does not rise dramatically, maybe that is just my misfortune. I do have high blood pressure (BP) on my normal and optimal dose of NDT but I increased it very slightly one day and my BP shot up to 200/70! I will never do that again!

Sertiko in reply to LAHs

Thanks so much LAHs, this is all a bit trial and error but I will monitor as you suggest and see what happens. Best wishes x

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