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Thyroid UK
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Hypothyroid and underweight? ?

I'm 17 years old and I was diagnosed with Hypothyroid and I'm underweight. My tsh level was 8.09. Ive been taking levothyroxine 25mcg for 13 days now. I go back to the doctors in March to do another blood test for the dosage and etc. Before I was diagnosed I weighed 87 pounds. Now i weigh 91.4 pounds witch is big for me cause I haven't weighed 90 for a long time, I now weigh in the 90s after taking my medication. I also don't feel so tired and lazy during the day anymore really. I was wondering if the levothyroxine is working and helping me gain weight and feel better.. and I was also wondering if being hypo and underweight is common? I look on line and ask yahoo answers and they tell me that it's impossible and they messed up.

I should weigh around 100 to maybe 105 pounds. I'm very petite and small framed, I'm 5ft. All I'm worried and focused on is getting healthy, feeling great and get my weight back. Should I gain weight with this medication?

14 Replies

Welcome to the forum. Yes it is possible to be underweight, I have seen posts on here which confirm that and hopefully someone will come along and share their experience with you. 25 mcg is a low starting point and doesn't always have much of an effect but the usual time to leave between tests when starting out is 6 weeks so I should go a little earlier for your blood tests so you can see what is happening. Has the doctor explained how to take your medication? It's probably easier to take is first thing as it needs to be taken on an empty stomach, 4 hours after any food. Swallow it with a full glass of water then wait an hour before eating. Keep 4 hours away from calcium and any other medication as they can stop you absorbing it well. Also when you go for your blood test stop your medication 24 hours before as it will give a false reading and get your appointment early in the morning if you can as TSH is higher then. When you get your next bloods post then and their ranges, important as ranges differ from lab to lab, and you will get plenty of advice. It can be a slow process to get things sorted because of the time to be stable on a dose before each retest so be patient. I would start a diary of your journey, wish I had, and note down symptoms, doses and results and any life style changes as useful to look back on.

In the mean time read what you can. Loads of info on the Thyroid UK site. Don't worry, it can be confusing but ask on anything you don't understand. No question is too trivial, we all understand as we have all been there! Everyone reacts differently so don't worry if what works for them doesn't work for you but we are here to help you every step of the way.



Yes it is indeed possible, it's one of the reasons my mums hypo was missed for years/decades. She's a size 10/12, not bad for her 80's. But she always was that size except when she was a teen.

As I understand you can get any of the symptoms/signs for either hyper of hypo for either condition.

I was missed for years because I had more than a third missing on my eyebrows, docs thought it had to be a definite third. It can in fact be a most of your eyebrows.

its good you are feeling better, it's been caught early then. I hope you continue to feel well.

Good luck



Yes it is possible!! :-D (I've been waiting to find someone similar to me)

I have been hypo for nearly a year now, I'm 23 and 5ft 2, when first diagnosed I was 7st 8 (106lbs) after a couple of months on Levo I dropped to 6st 9 (93lbs) - at the moment I'm roughly 95lbs and it's a constant battle to keep my weight up.

I have been to the doctors every 4 weeks since being diagnosed and gone from 25mg now up to 75mg. I have pretty much got my energy back (I was a marathon runner though and still am unable to run!)

I choose to have a paleo diet (no processed food) and make sure I have healthy fats from nuts, avocados and meats everyday.

Let me know if you have anymore questions, I know how daunting this all can be! X


The other day I posted this:


Muscle wasting can certainly occur in hypothyroidism. Note that the link specifically mentions protein intake. If muscle wasting is alongside putting on weight as fat and/or water (mucinous deposits) it is often missed.

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HI My Endo says that you can be Hypo and have all the symptoms of Hyper. I do.

Best wishes,



Hi, My husband is hypothyroid and has great difficulty in maintaining his weight. He likes to avoid gluten and potatoes as they tend to bloat him out. His diet is very healthy with loads of vegetables and moderate amounts of lean meat. He does not have cakes, bread or pastry so tries to maintain his weight with high protein nibbles ie. nuts natural yogurts etc. He hasn't found an answer as such but can just about keep a steady weight so long as he keeps up the protein. This problem has got worse as he gets older, he is 64 now but very active which adds to the problem, if he didn't do so much he could probably keep his weight on a bit easier. He does suffer from lack of energy but it seems to help by having power naps and a couple of squares of 85% dark chocolate a day. The dark chocolate definitely helps with the energy and low mood levels.

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I originally went to see my doctor due to my weight loss and tiredness and was diagnosed as hypo although they've now suspended my Levo as it was affecting my mood quite a lot O_o.

I now need to see an Endo as my doctor feels my problem may be my hypothalamus.

I guess we'll see but don't worry. You're not on your own.


I was diagnosed hypothyroid age 15 I am 47 now.

At the time of diagnosis i was 5 stone they thought I had anorexia and I am 4ft 11

I have always been petite and the heaviest I have been is 8 stone at the moment in weigh 7st 7.



Yes you describe me to a tea! This is an epic post, I'm sorry, but if someone had told me some of the things I was told at your age id have had a much easier ride over the last 20 years!

I became hypo aged 20 but I suspect I was already a bit, the contraceptive pill made me worse.

The way Janee describes her husbands diet is very much the diet I have always naturally preferred actually. Including the 70-80% dark chocolate!

At 18 I was seven and a half stone, 5'2". You may find at you get a little older that you do 'fill out' more though. My experience being petite and hypothyroid is that small changes can have a big effect. So it's worth becoming very strict about how you take it (don't get too hung up about it though! - remember a missed dose can be taken with the next one). I generally hover between 8 and 8 and a half stone now. When hypothyroid I do loose weight, I think it's actually because I loose muscle.

The amount of thyroxine your body needs is weight related. ive found I often have to change by 12.5 (ie half a 25 tablet); I've done this by alternating 125 one day and 150 the next.

I started on 50 aged 20. I actually didn't need thyroxine when I came off the pill, but then really needed it when I went back on a few years later and then probably lost all my thyroid during my 20s. I probably wasn't very well controlled during my 20s. I spent a year being extremely constipated which ended up being not enought thyroxine. I used to not be brave enough to know that I could ask the gp to double check results.

As you naturally don't hold fat (like me) it's worth keeping a record of Tsh (and t4 / t3 if they do it) and how you feel. Particularly muscle strength.

I'm currently recovering from a brief SLIGHTLY not enough thyroxine phase following the birth of my son. It's wrecked havoc on my muscles and I've been seriously disabled (though I'm waiting to find out if it's anything else). Part of the reason this happened is that I wasn't exercising any more. Hypothyroid myopathy affects the proximal muscles which is what I've experienced.

I think this is the BIGGEST piece of advice I can give to you - I'm 38 - when you feel better, yes eat a really healthy diet (protein and nutrient rich - up to you about gluten etc, personally i feel it's about 'rainbow' foods, nuts, seeds, eggs, protein, fats, etc - following gluten free does actually mean less nutrient empty foods. i love nibbling prunes and almonds and cheese etc during the day) but MOST OF ALL GET STRONG. Get your heart strong through cardio (skipping, swimming etc) but try to improve your muscles, especially upper body, being a woman. Interestingly, I've always enjoyed eating fat and skin from meat. Its probably got muscle and collagen stuff in it!

Sugar and alcohol DO make me put on a little weight though I will say!

I Started building up my upper body by chance aged 26 as I took up capoeira which involves lots of cartwheels and hand stands but it's the lack of this recently that has left my upper body weakened and then strained muscles. (Incidentally I couldn't do them at all at first! Lots of subborn persistence!) But the lack of this has led to really serious issues. I've had to work on expanding my chest and straightening out again. (So swimming is good for this too) Through capoeira I found yoga but specifically a type called forrest yoga which focusses on a lot of physio and core strengthening stuff too - a bit like Pilates. Pilates would be good to do too.

Really, at your age, choose activities which you enjoy, but be aware of lookimg after your muscles. I will add I hated sports etc at your age! I liked hiking, walking, cycling and riding. I found swimming hard as simply no muscles! But, as I say building upper body strenght had helped there.

Because it affects muscles so much, it's why ferritin (iron stores), b12, folate and vit d are important. You especially need iron for growing muscles. Hence a nutrient rich diet. (And dark chocoalte is nutrient rich!) but it might be worth asking your Dr to keep an eye on these levels too, especially if you don't feel great.

Being tiny it may occasionally mean you are on too much thyroxine - I've found this at times, especially when I lost a few pounds and was doing lots of exercise. It's a hard balance. But this means you need to be aware of the risk of osteoporosis (when you're much older) so weight baring exercise such as walking, team sports etc - capoeira!- is wise. Much of your bone density is laid down in the teen years so eating foods which contain calcium is good too (live yoghurt, fish etc) Google katy bowman / katy says alignment matters. She has excellent advice regarding muscles and bones etc.

I am awaking a rheumatology appointment regarding my muscles and , despite gp thinking this is all hypermobility related, I think it's mainly the impact that low iron and low thyroxine has had on me, plus long term stress trying to work and look after a toddler and the house with no strength!

It can take a good few months to fully recover from any myopathy. Abd too much thyroxine can also affect the muscles. Hence why many people would advise t3 aswell - however, I'm personally reluctant at the moment as it has a short half life, and if small changes make a big difference in me I don't want to upset the apple cart. On the other hand, it could be that I really do need the t3 to help. Also, as weight can be an issue I don't want to add t3 if it could affect this.

Before I investigate (battle) for t3 I'm going to see how I am on really good levels of iron, vit d, folate, b12 and regular exercise. I'm already feeling a difference with extra iron tablets. interestingly, I've put on a little weight since upping my iron etc but don't feel well yet. I can literally see and feel muscles returning, though it's an extremely painful process!

(Don't aim to be a body builder - just strong and healthy!)


What a great post! I am currently 6stone 10 and when first diagnosed got very frustrated about not being able to gain weight. I now follow a very nutritional diet (pretty much the same as yours) and although I don't change in weight much I feel so much healthier.


Gosh yes!

I was always underweight for my age starting from a teenager I weighed 7st and in my early twenties I was always 7 and a half stone , After my children were born I stayed a steady 8 and a half stone, but all of that time I was suffering what I know now was thyroid. My mother has it too and in my thirties I was tested but all the time they said that I had antibodies and my thyroid was working very hard to keep up but they did not give me medication.

It took me till I was 50 to make them realise that I needed help - after some serious infections and collapsing several times & getting taken to hospital. Since then I have taken Levo I am now 54 but I have felt better but my weight has slowly crept up since I went on Levo as I enjoyed my food more and could actually taste it! I now follow a gluten free diet as I started to have bad gut issues and have felt a lot better too. All this has been through my own decisions to take control of my body and make the medical profession listen - otherwise I would be still suffering today as my blood results were TSH 4.7 or something that they said was borderline but its made a hell of a difference to me.

I am now about 9st8lbs and am 5'4" so still not bad, but all those years of feeling terrible and it took all that time, the crunch came as well one day when I did not even have the energy to walk up a street in town & I knew I had to do something.

You take care and I hope everything works out for you.

Castlepoint :-))


I was diagnosed with hypothyroid and I am underweight but my labs look ok.


My daughter lost an enormous amount of weight in her teens and put it back on when on thyroid medication. Many people don't know that you can lose weight as well as gain it when hypothyroid.

I hope you carry on with your recovery.


I'm happy to hear that me and her are similar and that she gained weight while taking levothyroxine. I feel more confident.


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