Desiccated thyroid has roughly a 4:1 ratio of thyroxine (T4) to triiodothyronine (T3). In humans, the ratio is 11:1. A combination of various ratios of T4 and T3 might not provide benefits over T4 alone. Some controlled trials have shown inconsistent benefits of various ratios of T4 and T3. The use of desiccated thyroid is usually accompanied with the practice of dosing according to symptoms instead of dosing to achieve "ideal" lab results (e.g. serum levels of TSH). While there is debate as to what the ideal serum levels are, dosing according to symptoms often results in higher dosages. Most endocrinologists are opposed to these higher dosages as there may be risks of hyperthyroidism and osteoporosis. The preference for "natural" treatment seems to stem from philosophical belief as opposed to science.Arguments for desiccated thyroid include:

Desiccated thyroid contains all the natural thyroid hormones produced exclusively by the thyroid gland, including calcitonin which plays a crucial but still quite unclear role in promoting and sustaining bone density, however it is already used in therapy for osteoporosis when other treatments fail. Desiccated thyroid therapy can be combined with synthetic thyroxine (T4) to balance out the T4/T3 correctly. Chemistry
Desiccated thyroid has been described in the United States Pharmacopoeia for a century as the cleaned, dried, and powdered thyroid gland previously deprived of connective tissue and fat... obtained from domesticated animals that are used for food by man (USP XVI). In the last few decades, pork alone is the usual source.
Desiccated thyroid, also known as thyroid extract, is thyroid gland that has been dried and powdered for medical use. It is used to treat hypothyroidism. It is less preferred than levothyroxine. It is taken by mouth. Maximal effects may take up to 3 weeks to occur.Side effects may occur from excessive doses. This may include weight loss, fever, headache, anxiety, trouble sleeping, arrythmias, and heart failure. Other side effects may include allergic reactions. Use in pregnancy and breastfeeding is generally safe. Regular blood tests are recommended to verify the appropriateness of the dose. They contain a mixture of thyroxine (T4) and triiodothyronine (T3).Desiccated thyroid has been used since the late 1800s. It is usually made from pigs, sheep, or cows. It is available as a generic medication. In 2017, it was the 130th most commonly prescribed medication in the United States, with more than five million prescriptions. Usage has decreased since the 1960s. Medical uses
The American Association of Clinical Endocrinologists and the Royal College of Physicians recommend against the use of thyroid extract for the treatment of hypothyroidism. Concerns include the potential for adverse effects from superphysiological levels of T3 and the absence of long-term safety data from randomized clinical trials. They recommend levothyroxine as the preferred treatment. Some practitioners refuse to use desiccated thyroid.About 65 mg of thyroid extract is equivalent to 100 μg of levothyroxine.Arguments against desiccated thyroid include:

Desiccated thyroid preparations have a greater variability from batch to batch than synthetic ones.