Thyroid UK

Under active thyroid

Hi guys

I'm 40 years old and have an under active thyroid for the last 4 years. I started on a low dose of thyroxin and over the last few years has it been increased just lately from 125 mg to 175 mg. My question is I was feeling awful with lots of symptoms including extreme fatigue. Once my dose increased almost overnight I began to feel more human again, my sleeping in the day just stopped and I found myself with lots of energy all day witch was fantastic. Unfortunately this only lasted for approx 17 days ( as I kept a diary) since then I have began to go down hill again feeling like I used to feel but not quite as bad as before. Have had to start sleeping again also along with some of my other symptoms creeping back. Has anyone experienced this before can it be common to see and improvement then regress again? I am due to go back for bloods at the end of the month.

Thanks all

4 Replies

Yes, this is fairly common until you reach your optimal dose. Your optimal dose may well result in your TSH being below range because thyroxine is only replacing one of the hormones (which is then converted to make the others) and the feedback mechanism is broken now you have hypothyroidism, so the usual blood tests aren't that great at telling you if you are on the right dose. The best way is to go by symptoms. If your TSH goes below range, that is nothing to worry about and you are at no increased risk of heart problems or osteoporosis unless it goes below 0.03. If it is below range they will probably do a t4 test, which should be at the top end of the range for most people on thyroxine-only treatment.

Hopefully you won't need many more increases but you can expect to regress slightly after each increase until you reach your optimal dose.

You may want to get serum iron, ferritin (stored iron), folate, vitamin B12 and vitamin D checked too. All are required for optimal metabolic health and tend to be low or low-normal in hypothyroid patients due to decreased stomach acid (if you experience digestive problems, this is probably why).

You may want to check out the main Thyroid UK website for information here

Hopefully you will be back to full health very soon :)

Carolyn x


Hi Caroline,

Thanks so much for the information, I shall be taking this info with me to my doctors when I go for more bloods. So if they do a tsh test and that is within normal range then my dose stays the same as what it is now?But if I am still having symptoms they are just going to tell me that these symptoms are down to my depression which they have done in the past :( I don't fully understand all this I have a lot of reading up to do to try and understand my condition. I am Ireland is it my right to ask to be referred to an endo as in feel my doctor not much of a help.


You could ask for a referral if you are not feeling better, especially if they are saying you are on the right dose. If you are not feeling better it needs to be investigated. You might be able to convince them that an increase would help. If you have any trouble, let us know as I'm sure some of us will be able to provide you with papers/info to give to your doctor.


Caroline thanks so much for your advice. I am going to get my bloods done in the morning after 6 weeks on 175mg so I will be asking what they are testing, I know they will be checking my TSH levels and checking my T3 and T4 is that right? I will ask for a print out of what my bloods were like 6 weeks ago too and post them here.


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