How long does Levothyroxine take to work properly if you have had it for a very long time??

I just wanted to ask I have been on Levothyroxine 100mg for two months now and have noticed no improvement whatsoever. I am eating healthily and trying to walk slowly each day but my energy levels are always so so low. I had my blood test nearly a month ago which showed that my TSH levels had dropped considerably and that my FT4 and FT3 levels were all in range so they kept me on 100mg and I do not have my next blood test until April but I am not losing weight and I am still exhausted and feeling cold all the time. I am also on Paroxetine 40mg antidepressants.

Do you know how long it could take for Levothyroxine to fully work and are the antidepressants getting in the way? I am worried about reducing them in case I can't cope as I have Borderline personality disorder.

41 Replies

Hi It can take a lot longer if had hypo for some time. Sounds like you may need T3 also. What are your TSH, T4 and Free T3? How is your iron and ferritin? B12 and vit D and diabetes check? All go with thyroid and affect it.


Hi Jackie,

At my last blood test just under a month ago, my TSH was about 1.3, my FT4 was 16.9 and my FT3 was 4.30.

I have a doctor's appointment on Wednesday so I will request a blood test for iron, ferretin abs Vitamin D also. I was checked for diabetes earlier this year and it came up clear though I have no idea of my levels.

Hi Sorry you need ranges as all Labs are different. If FT3 is low in range be worth trying some T3, just a little with the levo, depending on other results.


Hi Jackie, my TSH was 1.71 (range 0.30-5.00), my FT4 level was 16.9 (range 9.00-19.00) and my FT3 level was 4.30 (range 3.25-6.21)

I doubt very much they will put me on T3.

HI I doubt it either but ideal would be less T4 and a little T3.

Best wishes,


Thank you

hi it took longer than 2 months for me to feel any improvement but I was on a lower dose and suspect i had been hypo for years! just had another increase and still need another. Ive heard it described as like filling up a tank so if you can imagine your levels of hormone slowly depleting over time then the reverse has to happen as in gradually building up and everybodys different. hope you feel better soon

Thank you so much, I have my doctors appointment tomorrow

After 6 months I still had some frustrating symptoms ,others had gone. After a year I was much better although now eighteen months on I still have a couple of symptoms that I can live with. There is no quick fix sadly. Docs will be unwilling to try anything if bloods are "normal" .

Yes, I think it will take a long time but I will request a blood test on Wednesday.

Still sound pretty hypo to me! My TSH was always in perfect range..even when I had lumps all over my thyroid! Once it was removed and I was given thyroxine, I didn't really get well. The doctor told me all of my problems were 'something else' as my thyroid was in range. But it was in range when I was really sick I say, he looks a little puzzled by my argumentative tone! ( the lumps all over my thyroid were only found when I had a CT scan)

To cut a long story short, 3 years after my thyoid removal, I continued to be unwell...just about getting through life..everyday a struggle. I went to see a private recommended endo, who took one look and said, you are clearly hypo. He started me on Armour thyroid, and the difference was instant. Like a light switch being flicked. Now..2 years on, I am continuing to get better, even when I had thought I was good anyway!

This subject gets my blood boiling. Why are the Doctors letting so many people go through life like that??

Yes I know, I hate doctors like that, I only have one doctor at my surgery who understands and she is an agency doctor.

Yes, I guess it can take a long time. Glad you are feeling better. Yes very true about the doctors. Mine are all in range too and yet, I feel so exhausted and depressed all the time. It feels so frustrating.

Hi Naturegirl 22, I am sorry to hear how unwell you still feel.

My GP told me 2 years before I would be better but that was because I had been undiagnosed and therefore untreated for many years.

However, like others have said, it sounds to me as if the Levothyroxine is not doing a good job for you and I'd follow the advice about making sure your levels of ferretin, D3, B12 etc are all good, good rather than just within limits.

If you have the energy to keep coming on here you'll see that people post very helpful articles and you'll discover the importance of the vitamins and minerals for, for example, conversion or uptake of thyroid hormones.

I am currently trying magnesium because low levels can apparently lead to tiredness, depression, brain fog, feeling cold and other symptoms very similar to hypothyroid and I've forgotten now but it might have been necessary for using thyroxine.

Others, with more knowledge than me, will give you clearer advice on the vitamins etc.

I hope you soon find the right road for you back to good health.

Hi thyr01d, I am going to request a blood test for my ferretin, D3 and B12 on Wednesday when I visit the doctor. I have been sleeping for most of the day. Can you just take magnesium without knowing your levels first? Yes, I will look out for the articles.

Thank you.

Other people will be able to answer better than I can about magnesium, what I read was that there is no reliable blood test. My own diet is so lacking in foods containing magnesium that I am taking it without checking.

Hope that helps, please take care, you sound a lovely person who needs others to come to a greater understanding of this condition.

Thank you so much, that is very sweet of you to say. I will check which foods are rich in magnesium. Yes, I understand what you mean.

Since sending the earlier reply I've been back to where I store useful info picked up off here (otherwise I can't remember it) and found this:

GPs make the mistake of prescribing anti-depressants in lieu of evaluating and treating the free T3.

Estrogen, calcium and iron bind some of the thyroid hormones and make them unusable

May be relevant to you?

Okay thank you, I will look into this.

I too have been on 100mcg levo for two months with absolutely no improvement. At my last GP appointment I asked for my antibodies to be tested and last week I had my blood test results which showed TSH and T4 was within range, my antibodies, however, were 449, the range was 0 - 9! This confirmed Hashimoto's and I am now waiting for an 'urgent' appointment with an endocrinologist.

I was told that with this result I won't feel any better and my symptoms will,remain. As you can imagine I am hoping my appointment with the endo comes through soon.

Never take a doctor's word when he says 'in range'. We need a TSH of around 1 or lower to feel well. Going gluten free can reduce your antibodies.

If you're told that's as good as it gets, avoid this doctor at all costs. You will get prescribed levo for hashimoto's but you can have swings and roundabouts with the thyroid gland producing either too much or too little thyroid hormones thus you will feel hypo/hyper at times, so I'll give you a couple of links which may be helpful for you.!stor...

"I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions"

Thank you so much for this. My TSH is 1.71 last time I had my blood test. I was tested for antibodies and I do not have hashimoto's. I will look at the articles thank you.

Wow, that is very high. I hope you get your appointment very soon. Good luck with that.

Antidepressants can interfere with the uptake of levothyroxine.

Two months is a very short time and you should have had an increase every six weeks till you feel much better with a TSH around 1.

Also your B12, Vit D, iron, ferritn and folate should be taken. Ask the GP for a free T3 blood test because if it is very low you won't feel too good. T3 is needed in all of our receptor cells and the brain contains the most. Some psychiatrists do use liothyronine (T3) for their patients for depression.

"II am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions"

I do want to reduce my antidepressants from 40mg to 30mg or 20mg to begin with as they have very bad withdrawal effects so I will speak to the doctor about how to do this safely on Wednesday. They will not increase my Levothyroxine 100mg as my results are all in range. I have my next blood test in April. My TSH level is 1.71.

Thyroid hormones need to be higher than "in range". In range just isn't good enough for someone with hypothyroid. Not all that hormone is getting into your cells, which is the problem. You need to be medicated until your symptoms go away. T4 is generally not enough by itself either, you need some t3 probably as well.

As for antidepressants, I would get off them if at all possible. It's not unlikely that your "borderline personality disorder" is a plain and simple thyroid disorder. I'll post a link to more info about stopping antidepressants below.

Hi superparrot, my annoying doctor said we don't look at the FT3 when I mentioned it and said it is the FT4 that is important and is what we look at and when I tried to question her on this as to why my FT3 levels had dropped for 5.60 to 4.30, she said that happens sometimes so I just left it as she was not listening. I am seeing a different doctor this Wednesday so hopefully I will have more luck. My Paroxetine 40mg antidepressants have extreme withdrawal effects so I will have to ask the doctor about how I can reduce them slowly over time, I will definitely not be able to stop them abruptly and need to know that I can cope okay so I will ask the doctor about reducing them to 30mg first. I cannot rush this. Thank you for the link.

I've also seen people get very good results eating more carbs, lots of omega 3s and probiotics, and doing yoga or pilates. Also, if you have silver fillings that is another whole kettle of fish...

Hi Naturegirl,

Looking at you previous posts, it appears that you have been recently diagnosed and have been prescribed 100mcg Levo for the last 8 weeks or so, is this correct?

GP's normally prescribe from a starting dose of 50 mcg and check your bloods every six weeks or so, increasing the dose by 25mcg until you receive an optimal dose. Your bloods should then be checked every six months until you have consistent results, then once a year.

If you were put straight on to 100mcg, maybe your initial result showed you were so low that your doctor felt it necessary, but it will take some time for your body to adjust.

It took 18 months for me to get to a dosage that made me feel (almost) normal and that was when my TSH was below 1.0 (my dose for the last 15 years is 275mcg).

Your TSH was 1.3 in October and whilst your T4 and T3 were 'in range', the T3 was at the low end of the range, which is probably why you still feel unwell.

Taking into account you previous posts about dieting, the diet you describe is not good enough to sustain you. Try eating protein (such as a boiled or poached egg) with a slice of wholemeal toast for breakfast, include some protein in your lunch and you will feel more energised throughout the day, and least likely to binge in the evening.

Ensuring that you have a good balanced diet, together with vitamin and mineral supplements (after the blood tests suggested by Jackie) will help you to convert T4 to T3.

If you are living away from home whilst at Uni, it's hard to ensure you eating healthily but it's worth the effort because it will ensure you future health.

At your next appt, explain to the GP how ill you still feel and see if he/she will consider increasing you levo to 125 mcg. Improving your thyroid symptoms will probably help improve your depression. It is very unlikely that you will be considered for T3 therapy so soon after diagnosis, but it is something to consider asking for further on down the line.

Best wishes, Maggie

Yes, that is correct Maggie. I had mild hypothyroidism but she didn't mention what starting dose I should be at, she just prescribed me Levothroxine 100mcg to start with and said to come back in 4-6 weeks time for a blood test which I did after 5 weeks. My TSH had dropped from 5 something to 1.71 not 1.3 sorry. My FT3 levels had dropped from 5.60 to 4.30 (range 3.25-6.21).

I eat quite healthily, I have toast with nutella and banana, boiled egg on toast, porridge or cereal for breakfast, I have fruit and a smoothie every day, I have a salad, soup or sandwich for lunch and then healthy dinners such as lamb chops with wedges and vegetables, chicken, fish, mash and different vegetables and I try and drink some tap water and redbush tea throughout the day and an options chocolate drink at night. I have only been eating much better like this for 1-2 months now. Before, I was eating very unhealthily for many years. I live at home and my uni is local to me in walking distance.

Yes, I will speak to my doctor on Wednesday. Thank you.

Glad to hear about your diet, hope I didn't sound like I was l telling you off! Good luck on Wednesday xx

Lol not at all Maggie, not in the slightest. Thank you so much. :) xx

I think they say it takes six weeks for the medication to begin to work, maybe longer if you've been underactive for some time. I'm interested that you were put on 100mcg from the start. My endocrinologist did that with me, which panicked my GP who thought I'd have all kinds of symptoms from being over medicated! I didn't have any, and just gradually began feeling much better.

It may be that your antidepressants are altering the way the Levothyroxine works.. Do you take the Levo on it's own with water an hour before food, and away from any other medications or vitamins?. Best wishes MariLiz

Hi MariLiz, yes I take my Levothyroxine with water and normally take it an hour before food but sometimes, it has been half an hour due to my early schduele and I always take it at least 2-3 before other medications.

This is just the dose that I was prescribed, I wasn't told why. I am glad you are feeling better.

What does "in range" mean? Could you post your numerical results with the ranges used by the lab?

hi, my last blood test I had was 5 weeks after starting on Levothroxine 100mcg which was about a month ago. Here are my results. My TSH was 1.71 (range 0.30-5.00) which was a considerable drop for me as before it was 5 something. My FT4 was 16.9 (range 9.00-19.00) which had increased slightly from 14. My FT3 level was 4.30 (range 3.25-6.21) which had dropped from 5.60. I am not sure why that is but these are my results. The doctor said I am not due to have another blood test until April.

I haven't seen a case like this: FT3 drops from 5.60 before starting T4, to 4.30 after. I think you should go back and ask the doctor why FT3 would drop when FT4 went up. If she can't provide a reasonable answer, then I would assume it's a lab error, and you should have the tests redone. In any case, your FT3 should be in the upper half of the range (4.7-6.2) for you to feel well; regardless of anything the doc said, T3 is the controlling factor for feeling well. If the doctor cannot provide a reasonable explanation for the FT3 drop, the quickest way to feel well is to tell her you need a small dose of T3 to take with your T4.

(The only thing that occurs to me, that could cause FT3 to drop, is a change in your TBG [Thyroid Binding Globulin] level. And I don't know why TBG would change after starting T4.)

BTW, have you already determined that all the usual nutritional things (vitamin D, ferritin, B12, etc.) are OK?

Hi, no I haven't had my vitamin D, ferretin and B12 measured but when I go to see the doctor on Wednesday, I will request to have a blood test for this.

I have no idea why this could be, all the GP said is that it is normal for the FT3 levels to go up and down and that it is in range. I tried to question her on here but she would not listen. I have an appointment with the doctor who diagnosed me with being hypothyroid on Wednesday so I will ask her about it instead.

I've been on thyroxine or the equivalent for 26 years now dosage when started 150 mcg been on 125mcg for the past 15 years I know it takes time for the thyroxin to take effect I was told when I went on it not to expect miracles, my problem which I had help with from the people on this forum was if I were to stop taking it good forum this one I also listened to my specialist and was patient when I first went on it 2 months is a very short time really but the benefit can be remarkable I at least lost the crawling through my skin feeling after 4 months then came on in leaps and bounds I don't think I have ever lost the tiredness thought that could be with me being diabetic it wasn't so I learnt to pace myself and rest if I needed to without giving into anything so when your energy levels get low if you can, rest and build it up again

Hi , I really feel for you as you are not alone. I have been down this road. The NHS standard if your blood are fine is to give you anti depressants. I have had them and still feel rough but a bit happier feeling rough , if that make sense. Now I am not a dr or have any medical training but you need to get your adrenal gland tested, you can pump your self full of T4 and if its not being carried around your body or converted to t3 then you will still feel bad. Now the big problem is the NHS does not recognise you adrenals as a cause and I am afraid you will have to find a dr that deals with this.

good luck

John C

Thank you John, much appreciated :)

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