Can levothyroxine work this quickly?


Going by my symptoms and a recent blood test, I`ve gone underactive after RAI. I`d been prescribed 50 mcg levothyroxine last week but knew I needed more. So this morning I increased it to 75 mcg. Within 2 hours I was at last feeling more like my old self and began doing a bit of housework, which is unheard of lately. After another hour, I`d had enough and all the old hypo symptoms returned.

Anyway my thyroid nurse was due to phone me this afternoon, and I was rehearsing all day on what to say to get my levo increased.

She called and had shown my blood test to a consultant who suggested I raise to 75 mcg ( so the rehearsing was for nothing :))

I confessed that I`d raised my dose and asked if it would work so quickly and she said no! So I`ve come to ask you all- the people who really know :)



15 Replies

  • JoyLiz, no, your thyroid nurse is right. It takes 7/10 days to be absorbed and start working so it is probably the 50mcg you have been taking which is kicking in. It takes 6/8 weeks to metabolise properly to work on your hypothyroid symptoms. Try and pace yourself because overdoing it on days you feel well will leave you exhausted and set you back.

  • Thanks Clutter, yes I thought afterward that it does seem a bit quick. Anyway it`s good to know the levo is beginning to work. I`ll pace myself too.

  • After you've been on 75mcg for around 6 weeks and you feel symptoms returning, it is time for another blood test and increase. Some people need to take around 200mcg to feel better, particularly if they have had a thyroid gland removed. Even better would be for the GP to add some T3 instead of a rise in T4.

    On the days you get a blood test for thyroid hormones, don't take levo beforehand. Take it afterwards as it can skew the results. Take levo with a glass of water and don't eat for around 1 hour. Take supplements other medications 4 hours later.

  • Thank you shaws

    My thyroid nurse is sending me a blood form so that I can have a test sooner if the symptoms return. Hopefully now that I`m on 75 mcg things will improve.

  • It is still a low dose but it is best to increase gradually. Before the blood tests a normal dose of thyroid medication was between 200mcg and 400mcg. You always know when it's too much as we feel very overstimulated and we just either miss the next day's dose and then reduce the normal daily dose by around 25mcg.

  • Thank you

    One thing though is concerning me. When speaking to the nurse she said the ultimate dose is 150 mcg, surely this can`t be right?

  • They make assumptions, I am afraid. Everyone is different - we are not robots or machines that we have exactly the same replacements as a car etc. would. We are short, tall, fat, thin, so it stands to reason our medication will/should vary. The purpose of thyroid hormones is to have sufficient for our metabolism to be normalised so that we can function normally. The more we learn, the more we realise that the medical profession is not fully aware of how best to treat us.

  • Very true, thank you.

  • Joyliz, the ultimate dose is that which restores a patient to euthyroidism. Unfortunately the medical profession considers a patient euthyroid when bloods are within range. Patients think it is when their symptoms are resolved. Your thyroid nurse may mean that 150mcg is the limit she may prescribe and higher doses need sanctioning by an endocrinologist.

  • after Graves and then RAI your body has taken a battering

    plus all your vitamins and likely ferritin and folate will be very very low

    you need to boost them all with a good multivitamin olus iron and vit c if ferritin is low

  • Here is my flatly contradictory view!

    In some people, in some circumstances, an effect from a levothyroxine tablet can be seen within ten minutes. The person taking it might notice sooner, but I swear absolutely to have witnessed this on many occasions.

    What it doesn't and can't do is have its full potential effect. Taking, say, a 25mcg tablet might do something within minutes, and carry on for a few hours, then end up leaving the person as if they had not taken it at all. Or even worse off.

    From my own much repeated experiences, if I take Mercury Pharma levothyroxine, I know that I have taken it within two hours, probably faster. I feel over-dosed. This does not happen with Actavis levothyroxine. (But that simply leaves me feeling permanently under-dosed.)

    So as to be clear what I am saying and not saying:

    The full effect of a dose change can take weeks to reach. Indeed, I suspect that in people close to optimal dosing, the effects might ripple on even after months or years on a stable dose. No-one is going to recover fully in hours.

    The effect of a dose change on TSH levels can start quickly, but the full effect - ending up with a fairly stable TSH level - can take six weeks or more. I suspect that a lot of the effect occurs much quicker than that but I would rather have that backed up by proper research. This is one reason that doctors usually refuse to re-test sooner.


  • I agree with you. I find if my body is crying out for more thyroxine and I take some extra I can feel the difference almost straightaway. However it doesn't last very long, and it's not until I have been taking the higher dose for a week or so that I feel good all day.

  • My own experience also leads me to agree with helvella and eeng...

  • Hmmm thank you everyone, I expect we all react differently over the meds.

  • My experience tells me that we may all be different in terms of how quickly T4 gets absorbed. I take 125mcg daily plus an extra 25mcg when I do long cycle rides. This extra dose, taken before breakfast really does make a difference by lunchtime, which is the time I clearly run out of T3 if there isn't enough to convert. Also, I've read that our T4 level peaks 2 hours after taking it, so it clearly gets into our blood within two hours. I suppose that no reasearch has yet been done to work out how long it takes for the cells other than blood to make use of the T4. Taking our morning dose before a blood test wouldn't make a difference if it took a week or more to be absorbed. It seems to be another area in which we all have to find out what works for us. I can tell when I forget to take my extra dose before a cycle ride, and it's not psychological, as I only realise after wondering why I'm struggling to cycle, and then I picture myself taking the morning dose, and realise I've forgotten. It all needs to be worked out by analysing each person individually. Doctors have to use their clinical skills if they want to get it right for us.

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