Jen15 Well, it's clear that your doctor is dosing purely by TSH alone. There was nothing in your first results that indicate the need to reduce your dose of Levo. Your FT4 was in range, you were feeling good and that reduction in dose has brought your TSH up, reduced your FT4 considerably and you now feel symptomatic. So you need to put up a bit of a fight to get your former dose reinstated.
From ThyroidUK's main website > About the Thyroid > Hypothyroidism > Treatment Options:
"According to the BMA's booklet, "Understanding Thyroid Disorders", many people do not feel well unless their levels are at the bottom of the TSH range or below and at the top of the FT4 range or a little above."
You can buy that little book from Amazon, about £4.95, or maybe your local pharmacy. Show the appropriate part to your GP. Point out that the book is published by the British Medical Association.
"Dr Toft states in Pulse Magazine, "The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.
In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance.
But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.
This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."
Dr Toft is past president of The British Thyroid Association and leading endocrinologist. You can obtain a copy of Dr Toft's article by emailing email@example.com . Print the article, highlight question 6 and show to your GP. Ask for an increase in your Levo dose as you wish to get back to where you were before - symptom free. If he isn't happy, ask for a 3 month trial back on your original dose and he can then retest. When retesting, if your results are similar to those that caused him to reduce your dose and he wants to reduce again, tell him you want FT3 tested to see if you are in range, as mentioned in Dr Toft's article.
In case you don't already know, when having thyroid tests it should be at the earliest appointment of the morning, fast overnight (you can have water), and leave off Levo for 24 hours. This gives the highest possible TSH which is what is needed for an increase in dose or to avoid a reduction.