Eating cabbage twice a week made me do some searching and I found that cabbage contains goitrins, which is one of the three types of goitrogens:
goitrins, thiocyanates, and flavonoids.
I also found that "Foods that contain goitrogens are able to disrupt thyroid function by inhibiting your body’s ability to use iodine. More specifically, goitrogens can block the process by which iodine is incorporated into the key thyroid hormones thyroxine (T4) and triiodothyronine (T3).3
They also inhibit the actual release of thyroid hormone by your thyroid gland and disrupt the peripheral conversion of the thyroid storage hormone T4 into the active thyroid hormone T3.
As a result, goitrogens can cause a goiter or an enlarged thyroid. They can also act like antithyroid drugs, slowing down your underactive thyroid and potentially causing hypothyroidism."
So if it were me I would not want to take thyroid med unless I was sure about the cause. I would investigate the possibility of it being related to eating cabbage so often, by stopping it and after several months, re-test your thyroid function. Specifically, you should test for the active thyroid hormones, Free T4 and Free T3 (not Total T4 and Total T3), and TSH again. Note that TSH is useful as an indicator of thyroid status only when it is at extreme levels. The best indictors are an evaluation to determine if there are multiple symptoms typical of hypothyroidism. If those symptoms are present, and Free T4 and Free T3 are in the lower half of their ranges , that is strong evidence of hypothyroidism and the need for thyroid medication. Also note that if you need thyroid medication, the dosage should never be determined based on TSH. Med dosage should be enough to relieve hypo symptoms. Also if you should have to take thyroid med, make sure you delay your morning dose of the med until after the blood draw for thyroid tests, in order to avoid false high results. If found hypothyroid, you should also test for Vitamin D, B12 and ferritin and supplement as needed to optimize. D should be t least 50 ng/ml, B12 in the upper part of its range, and ferritin should be at least 100.
Yes it is absolutely sage to stop the thyroid med after only one dose.
Other than for some types of hypothyroidism that are temporary, If a person becomes hypothyroid then yes the medicine is needed as a daily replacement for life, and after long term use, stopping the med would cause a return of hypothyroid symptoms.
I don't know for certain how long it will take for your thyroid system to reflect stopping the daily intake of cabbage, but if it were me, I would wait for several months and then re-test and see if your thyroid levels have changed.
Test results vary from one lab to another, so you always ned to compare results to reference ranges from that lab. So please post the reference ranges for those results.
Also, have you ever been checked for the antibodies of Hashimoto's Thyroiditis? Since your original TSH was high, it would have been good to test for Thyroid Peroxidase antibodies (TPO ab), and Thyroglobulin antibodies (TG ab) Those tests would tell if your high TSH was due to Hashi's, and you need thyroid med. If the high TSH was due to all that cabbage,the you don't need the thyroid med.
Also did the doctor test for Vitamin D, B12 and ferritin?
You really cannot know the cause for your high prior TSH unless you get tested as I suggested previously: "Since your original TSH was high, it would have been good to test for Thyroid Peroxidase antibodies (TPO ab), and Thyroglobulin antibodies (TG ab) Those tests would tell if your high TSH was due to Hashi's, and you need thyroid med."
Until you get those additional tests done, it is not a good idea to suggest anything about your test results. and medication dosage. In addition please tell us about any symptoms you have currently.
Hashimoto's Thyroiditis is an autoimmune system dysfunction which which the body erroneously identifies the thyroid gland as foreign to the body and produces antibodies to attack and eventually destroy the gland. As the gland becomes unable to produce enough thyroid hormone, the FT4 and FT3 levels drop while the TSH increases significantly. If Hashi's is the cause for your hypothyroid symptoms, high TSH and relatively low FT4 and FT3, then replacement thyroid medication is necessary. This is why you need to test for the antibodies of Hashi's, to see if that was the cause.