In fact, thyroid hormones have been used to augment antidepressants and convert nonresponders, and to treat certain rapid cycling and hypomanic patients unresponsive to other treatments (though careful medical evaluation is essential, as thyroid hormone may promote mania).
In some bipolars, thyroid activity cycles with affective state. Bipolars may be particularly sensitive to such fluctuations, even when within the normal range. (Cole 2002) Cognitive function, for instance seems to be significantly linked to thyroid status, rather than lithium levels. (Tremont 1997)
Barnes (1976) warned that many patients medicated for depression, anxiety, and so forth, have undetected thyroid dysfunction, causing mood symptoms. Unfortunately, effective thyroid status is often obscured by distorted interactions of the hypothalamus/pituitary/thyroid axis, and by difficulty determining peripheral sensitivity to thyroid.**(Pies 1998)
* Even as compared to the general psychiatric populations, in which thyroid problems are common. (Gloger, 1997, Fardella 2000, Placidi 1998)
** For example, you can get high thyroxine, with an elevated pituitary TSH nonresponsive to regulatory feedback, so continuing to stimulate the thyroid further. Along with high thyroid symptoms of, for example, weight loss, rapid heart beat, etc., the patient may manifest selective insensitivity to T4 in mood-modulating neural pathways, fostering the low thyroid symptom of depression. Labs also will be contradictory: with high T4, suggesting hyperthyroid; high TSH, hypothyroid. Thus neither effective thyroid status nor appropriate treatment will be readily apparent.
Hypothyroidism characteristically creates a depressive syndrome; even subclinical hypothyroidism may be associated with mood cycling, depression, and poor or slow response to affective treatment. Autoimmune thyroiditis is often associated with depression (especially postpartum), and with rapid cycling. Hyperthyroidism creates symptoms of, and contributes to, mania. (Pies 1998)
Nonetheless, the precise impact of thyroid activity can vary from one individual to another. (Loosen 1987)
I have excerpted the above post from the first page of a 32-page section on thyroid in my book, Natural Healing for Bipolar Disorder (copyright 2009).
To get a comprehensive view, you may want to look through my book, on bipolar disorder
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Reminder: This information is presented for educational purposes only, and is not intended as diagnosis or treatment recommendations for the individual. Each person's biochemical requirements tend to be unique. So if you need treatment for bipolar, thyroid disorder or any other medical condition, please consult a knowledgeable physician.