Hey guys, a little background info first.

A week and a half ago, my TSH levels were around 6.1. My GP did an ultrasound on my thyroid and it was slightly enlarged. She put me on 25 mcg/day and we're going to check levels again in 6 weeks.

What I'm wondering is if anyone's ability to exercise (specifically cardio) was affected once starting levothyroxine?

Due to midterms, I hadn't done much cardio since I started the meds. I got on the elliptical yesterday and wasn't able to go for more than 5 minutes at a moderate pace when two or three weeks ago I could handle at least half an hour and moderate/slightly hard.

My heart rate was in the 140s after about 2 minutes. I thought it might have been the coffee I had yesterday (like I said, midterms), but it happened again today when I haven't had any caffeine.

Anyway, all my other parameters have always been excellent (bp, heart rate, cholesterol).

Has anyone had a problem with a drop in endurance/rise in heart rate when starting levothyroxine?

Caveat:
I'm a pharmacy student and I have looked through the package inserts and my textbooks. I understand the mechanisms about why this could be happening, but my doctor or any other friend's i know have never mentioned this being a side effect.

Maybe I just don't look like I generally do lots of exercise.

Anyway, thanks guys.

Zen, I take a fairly high dose of Levoxyl (I alternate .175 and .200) and haven't noticed any effect on my daily exercise and HR. We're all different though, especially when it comes to meds!

I have noticed, though, that a 2 - 3 week layoff has a huge effect on cardiovascular conditioning in most people. If that is what's going on with you, be assured that it comes back quickly. But don't be surprised if it takes a week or more of pushing a little farther each time to get back to your half hour on the elliptical.

My suggestion is to keep doing the elliptical for a week and monitor your HR and endurance each session to see if it's the meds or layoff that's affecting you.
Good luck!

My only thoughts are that if your thyroid levels are too high (if you were taking a dose that was too high), that might affect your heart rate. It took me a long time to have the dosage adjusted to be perfect for me and when I started on the medication, it so high that I got dizzy if I got up too fast and fainted once before it was fixed. I think it might be like Meg suggested though, as well.

See how you're feeling and otherwise just go for a blood test. It's a simple fast way to see how your levels are. I'm not sure though if a couple of weeks is enough time to see a real difference.

You can always call your doctor if you're concerned.

Did you have any other symptoms like shortness of breath?? I alway notice when I become short of breath I am retaining more water and my TSH needs adjusting. My heart rate actually is much lower due to the hypothryroid along with my blood pressure. I actually have to exercise a min of 15-20 min befire my heart rate increases to my target heart rate. So hmm I'm wondering...you know I was on leverthyroxine and experienced some side effects and when I changed to my new Endo he changed it Levoxyl..and so much better for me. I was having palpitations and just yuck. I've heard others complain of this too. Maybe call your doctor...if you haven't already.

I take 300 mcg of Synthroid and it doesn't affect my exercise at all. I exercise at Curves 6 days a week and walk. You are on a very tiny dose. Unless you don't need any, I can't see it affecting you. Check with your doctor.