Thyroid UK
87,597 members102,305 posts

I've had radio iodine treatment and started piling weight on fast .. Is that normal ?

Hi I had my treatment nearly 3 weeks ago I've put on over 1 lb per day for the last 5 days and I'm worried if this continues I will have a serious weight problem .. I spoke to the thyroid nurse today and she didn't really give me any answers .. I'm having a blood test on 19/ 12 but its concerning me .. I don't have any other symptoms to speak of .. Has anyone else had this ? Thanks Mandymoo

8 Replies

Yep it's normal.. Presumably you were hyper which is why they gave you radio iodine and now you're Hypo

Take your temperature, that will tell you how Hypo you are..

Weight gain IS a symptom, so is low temperature

You need some supplementation.. tell GP asap about the rate of your weight gain... and get yourself on a LOW GI diet asap

Good luck...


yes its result of RAI and hypothyroid hitting but you will need to remind them of old swedish research where after Graves Disease the body is so sensitised to high levels of thyroid hormone that blood tests cannot be relied on

you have to be treat on symptoms because your body cannot function on so called "normal " level

Free T4 will need to be right at top of the range or just over it TSH is irrelevant


I assume you are on some medication or do you have to wait a certain length of time? If you have been given some, what is it and what dose? It takes a while to get the dose right but certainly would not expect you to put on a pound a day. x


Thank you for the advice .. Yes I was hyper

The nurse made nothing of it so I wasn't sure but I will start taking my temperature and the low gi diet ..

Thanks again


I'm on 50mg of propylthiouracil and been told to continue with it until my blood results on the 20th .. I just hope things settle down


Hi mandymoo. I was hyper and had RAI treatment. Like you I was told to continue anti thyroid medication and given very little information. Within a short time, while waiting for my next appointment to come through, I became severely hypothyroid.

It sounds stupid now I know much more about thyroid conditions but I didn't realise what was happening to me probably because the after care was negligent and I was given no information - they were totally dismissive as if it was no big deal and no need to ask questions.

That put my guard down. My husband couldn't wake me up one morning (about three to four weeks after RAI) and I was taken to hospital with hypothermia caused by myxedema coma.

All I remember was going to bed the night before with hot water bottles because I was like a block of ice. I lay there realising I was having an out of body experience but was so calm I just didn't care if I lived or died any more. That feeling of calmness was a blessed relief after years of extreme hyper activity.

They were totally dismissive of this negligent follow up after RAI treatment.

The reason I tell you this is because I thought they knew what they were doing and trusted them. I now know my judgement was shot to pieces. In many cases RAI treatment can take a while to start working so they think you can just be left on anti thyroid meds and follow it up at their convenience with blood tests.

How wrong that was. RAI can start working very quickly - the dose is guess work. On top of that with anti thyroid drugs too you can quickly go hypothyroid.

The blood tests are only a guide especially while the body is adjusting and signs and symptoms should be monitored.

Your rapid weight gain is one sign your metabolism is slowing down - you need to check your body temperature and pulse for other signs. Other typical symptoms of hypothyroidism can take longer to show up - like dry skin and brittle hair so are not a good marker.

In your shoes I would insist on blood tests now to get an indication if you are already hypothyroid. If the RAI has started to work already its logical they should stop the anti thyroid meds now.

Unfortunately it's a sad fact that care and knowledge of thyroid conditions in this country is in many cases abysmal. I suffered needlessly and so did my young family because I didn't know that and didn't take control of my own health and treatment. After learning the hard lessons, I took ownership and eventually got my health back without their involvement except repeat prescriptions. You can and will get better.

Hope you are on the mend very soon x


By the way - I meant to ask - could your rapid weight gain actually be fluid build up? Are your legs or ankles puffy? When metabolism slows down too much body fluids including urine excretion can slow right down too and cause a build up in the tissues. That is a sign of hypothyroidism.


Hi Editfrmt , thank you for the info , I'm sorry to hear what you went through it sounds extreme and very frightening

Having just weighed myself I've gained yet another pound this morning and I'm ringing my G.p asap as I'm not happy to wait until the end of next week for a blood test ..

I understand completely about the dismissiveness after the RAI , when I rang I was told not to get 'hung up ' on the weight gain but it's an obvious indicator that things are changing dramatically .. And I've just had a hip replacement so weight gain has to be monitored .. I will start taking my temperature and as you said I will start taking control of my health myself and listening to what my body is telling me ..

I haven't noticed that my legs are puffy but I definitely don't pass urine like I did and im bloated so I think water retention my have a small part of my weight gain but I'm a small framed person so it's becoming quite obvious that my body is growing rounder

I'm glad things have settled down for you and your family and will look forward to getting past all this .. I'm wishing I hadn't had it done now in some ways

Thanks again x


You may also like...