Thyroid UK
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Thyroid changed

I have been taking .75 Synthroid for years which kept my thyroid level at .1. I felt great and was at normal weight. I quit smoking and my system seemed to just go haywire. My thyroid level went up to 3.3 and I have gained a lot of weight, tiredness, trouble breathing since. It has been 1 1/2 yrs. since I quit smoking and thought everything would settle down but it hasn't. My doctor says 3.3 is perfect. Does smoking effect the thyroid that much?

9 Replies

I don't know about smoking doing that, but if your perimenopause/menopaused./post menopause...or anything hormonal (had baby etc) might do that...or lots of stress...

I was on 0.75 of synthroid (levo) forever, then things went wacko...I was too busy at first to be tested Mom was dying, menopause was arriving, daughter leaving home etc...I think most of all the hormone thing triggered it off....3.3 is just over the line with what feels normal or good to me.....Many labs say up to almost 5.0, but if you start to feel crummy you let them know that's not good for everyone, were not all the same! They might say its a fine ok reading at 3.3, but really they might be waiting to see what it does next. They left me for a year, and I gained 35 pounds(Im in Canada)...and I was no where near the reading of 5.0, and I felt crummy an very tired, and a little depressed.


If you felt well on a previous dose that kept your TSH at 1 and you are now at 3.3 the doctor should have increased your dose to bring your TSH in line as previously. When taking levothyroxine, its 'how you feel' that's the most important not whereabouts of the TSH level.

Many doctors think that if the patients TSH level is within the 'range' that they are on enough medication and that any clinical symptoms which come back have nothing to do with the thyroid gland. They're wrong, clinical symptoms should be used as well as a blood test for diagnosing a thyroid gland problem. Nowadays it seems to be diagnosed on the TSH alone and given other prescriptions for the symptoms rather than a decent dose of thyroid hormones..

Most of us feel well with a TSH at 1 or below, or suppressed.

You need an increase in medication.


Yes smoking does effect the thyroid. It's known to increase T3 in the body, in effect making you feel better. Hense, when people give up smoking they put on weight, suffer from tiredness. For some this means they get diagnosed in the first place.

From a personally point I gave up smoking in the 1980's, I put on weight , struggled more to get up in the morning, my hair started thining. However it was also a stressful time so that's what was thought was the reason.

The smoking T3 link has been written up into a medical paper, I will try and find it.


Starfish123, is this the research that you're thinking of:

"Serum triiodothyronine (T3), thyroxine (T4) and thyrotropin (TSH) concentrations and urinary thiocyanate levels were examined in healthy smokers and non-smokers as an indicator of smoking behaviour. Smokers were subdivided into moderate and heavy. Significant differences in urinary thiocyanate levels were apparent between all three groups. For heavy smokers, serum T3 concentrations were significantly above the values found in non-smokers. Increased serum T3 levels were not accompanied by a substantial change in serum T4 and TSH concentrations."

As T4 and TSH levels weren't also changed, I wondered if the high levels of T3 indicated that it was pooling in the blood rather than being taken up by the cells?

However another research found "Substantial decreases were found in serum thyroxine (T4) and triiodothyronine (T3) concentrations in heavy smokers compared with nonsmokers. Reduced serum thyroid hormone levels were not accompanied by a substantial change in serum thyrotropin concentrations. The free T4 index, free T3 index, and T4-T3 ratio were not substantially different for either group."

A more recent study found: "Active and passive exposure to cigarette tobacco smoke is associated with a mild inhibitory effect on the thyroid reflected in higher serum T4 and T3 in nonsmokers, compared to smokers in this cohort of women."


That is very interesting Starfish123. I had been borderline for several years but 2 months after giving up smoking I was tested as having a TSH over 100. I always thought there must be a connection


Yep. I gave up smoking in August last year after 45 years and by Christmas I crashed - most of the classic symptoms of hypo, even though it is strong in my family - It definetly had an effect - I have been smoking a bit recently - I alternate between e-fags and tobacco xx


I have a 23.0 thyroid been giving me 50mg a night been refusing it what happens to me


This seems to be common ....smoking makes people better who are hypo and suppresses the TSH. Sorry but I don't recall the mechanism of action but it seems to be very common.


Hi all, I studied the subject of smoking as part of a course recently and smokers have higher levels of cortisol in their blood than non-smokers and believe it or not this has some benefits. Cortisol in sensible doses gives you get up and go (low cortisol and you want to sleep). It might not be anything to do with hypothyroidism, but the cortisol. However, high and constant levels of steroid hormones, such as cortisol, interfere with thyroid function. So it's a very happy medium that should be aimed for. It might be an idea to get your cortisol levels checked out.

best wishes


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