T4 (Thyroxine)

Thyroxine (T4) is a hormone produced by the thyroid gland, with a ratio of T3 to T4 in healthy individuals typically higher than in those taking synthetic T4 supplements 3. The thyroid gland releases T4 and T3 in a ratio of approximately 4:1 or 5:1, with the liver completing the activation of T4 to T3 in the body 3. However, in hypothyroid states, a higher ratio of T4 to T3 can lead to the inactivation of T4 into reverse T3 (rT3), exacerbating symptoms 8.

The use of synthetic T4 (thyroxine) as a treatment for hypothyroidism has been criticized by some, as it can suppress the conversion of T4 to T3 in the liver, particularly in women with high estrogen levels 2. In fact, women may experience worsening symptoms when taking T4 supplements, as it can turn off the conversion of T4 to T4 and suppress the TSH 2. In contrast, T3 has been shown to be effective in alleviating symptoms in both men and women, particularly in cases where T4 is not sufficient 4.

The study that led to the substitution of T4 for the natural combination of T3 and T4 was conducted on young male medical students, who did not have the same thyroid problems as women 6. However, this study has been criticized for its limitations, and many experts now recommend a more individualized approach to thyroid treatment, taking into account the unique needs and characteristics of each patient 2.

In some cases, the use of T4 supplements can even lead to adverse effects, such as hypertension and cerebral hemorrhage, particularly in women with hypothyroidism 7. Therefore, it is essential to carefully consider the potential risks and benefits of T4 supplementation and to work with a healthcare professional to determine the best course of treatment for each individual.