Thyroid UK

Increased Heart Rate with NDT

Hello everyone, I have been on NDT for the last 6 months and feel like I have got my life back. Got so much more energy and almost all my old hypo symptoms gone. According to the endo, the blood tests and the way I feel I'm pretty much at the optimal level of NDT now at 3 grains, split to 2 in the morning and 1 in the afternoon. My irregular heart palpitations have disappeared since I swapped Levothyroxine to NDT, however I have been increasingly noticing elevated heart rate - my pulse can go up to 100 and over in an instant from not any particular activity! My heart can be pounding like crazy while doing the dishes or resting. My head also feels a bit whoozy and I get out of breath.

Can this be caused by the intake of NDT, is this a T3 rush? Or could having low iron stores be the cause? I know my ferritin is right at the bottom range. How can I tell if I am taking too much and actually being hyper, or if this is something else?

Anyone with any ideas please help!

Thank you so much,


6 Replies


You should have a TSH, FT4 and FT3 tests to check you are not over medicated.

1 like

Thanks Clutter, my last test results were:

Free T4 = 10.1 pmol/L (range 10.1 - 30.2).

Free T3 = 6.40 pmol/L (range 3.56 - 9.35).

TSH = < 0.097 mIU/L (range 0.465 - 4.68).

How does that look, according to the endo it's good?



Can you check the FT3 range, I've not seen FT3 higher than 7.0.

If the range is correct you are not biochemically over medicated but you could try reducing dose by 1/4 grain to see whether the heart pounding and breathlessness improves.


Thanks for taking time to reply and to help out!

The FT3 range is correct indeed, says 3.56 - 9.35 in the lab print out.

Still waiting for results from the test I had last week so will get the latest update soon! I also want to keep log to see what times in the day I have the pounding, as it might have something to do with the NDT peaking times.



T3 can raise heart rate about an hour or two after ingestion. It will usually subside within another hour or two.


Years ago, before the invention of the horrid tsh test and synthetic T 4 thyroid hormone, docs treated by symptoms, heart rate and body temp. When you keep that log, do take your body temp and record heart rate at about 3 pm each day. Also record your dosage and how you are feeling....nothing fancy or burdensome, just jot down the numbers.

The T 3 might be finally building up in your system so, as some suggested, maybe cut back the NDT by 1/4 grain and see how your heart rate/body temp responds. It wouldn't hurt to get your D 3, B 12 and iron levels checked. It can be almost impossible to regulate NDT dosages if these other nutrients aren't optimal in the body.

Just an aside... I tend to react with heart poundings when I ingest some food additives, specifically, caramel color, Blue # 1, Blue Lake and FDA Yellow # 5. I know... Even my cardiologist thinks it is weird. But it is what it is. Point being, maybe note what foods you have eaten within 15 - 20 mins of your rapid heart beat episodes. Maybe a connection?

1 like

You may also like...