Natural Thyroid which contains both T3 and T4 is a more robust and safer thyroid medication when compared to T4 only medications such as levothyroxine and Synthroid. This is an obvious conclusion, after 10 years of clinical experience prescribing Naturethroid, as well as converting many patients from Synthroid to natural thyroid. In addition, this information is clearly demonstrated in the mainstream medical literature as well.
In addition, the TSH test is not a reliable indicator of adequacy of treatment. In other words, when the patient is taking the proper dosage of natural thyroid medication with complete relief of symptoms, the TSH will typically fall below the lab reference range, also called a suppressed TSH. This will disturb the mainstream clinician who mistakenly believes the patient is taking too much thyroid medication. The issue can be settled simply by running a Free T3 test which will show that the Free T3 in the normal range, thus excluding any possibility of a "hyperthyroid state".
Many patients do quite well on Synthroid. However about 20% (one fifth) of patients on T4 only medications like Synthroid do not do well, and have continued symptoms of a low thyroid condition.