Due to the disorder in the endocrine system sometimes the thyroid gland does not produce enough thyroid hormone and there is a deficiency of it in the body and this condition is known as Hypothyroidism or under active thyroid or low thyroid. This is a serious condition in the sense that a patient has to take life long external thyroid supplement like one which you have mentioned in your query.
When a person is having problem of Hypothyroidism then he can have symptoms like feeling of tiredness, constipation, depression, weight gain and reduction in ability to withstand cold. This ailment lowers the metabolism of the body and then relatively more calories are to be burnt for the specified weight loss.
The experts in the nutrition and life style suggest that adding iodine loaded foods like seaweed (wakame or nori), yogurt, iodized salt, saltwater fish and eggs can help in regulating the thyroid hormone in the body.
The research in food and nutrition in thyroid affected people suggests that a healthy and well balanced food is the key to thyroid management and bananas, ginger, fermented food, lemons, probiotic supplements, avocados, pears, plums, citrus fruits, apples, extra-virgin olive oil, sunflower oil, coconut oil, nuts, nut butters, Vitamin B, Vitamin C and Zinc in some form - all of these are in one way or other helpful in thyroid functions. Especially the pears, plums and apples which are rich in pectins and help in removal of heavy metal elements from the body because these heavy metals like Mercury are linked with the Thyroid malfunctioning.
It is also told that one has to limit the consumption of cauliflower, kale, turnips, brussels sprouts, cabbage and boo choy because research suggests that presence of these foods in the digestive system of the body reduces the body's ability to utilise iodine which is an essential element for thyroid functioning.
By adopting a well balanced life style and consuming selective foods one can achieve improvement in ones thyroid functioning and in many cases it is seen that the dependency on external thyroid supplement is reduced significantly and its doses are accordingly reduced by the doctor.
So one has to take opinion of the doctor in this regard at specified time intervals and get the thyroid tests done so that he can prescribed the correct dose of external thyroid supplement.
Knowledge is power.