The cause of hyperthyroidism (overactive thyroid) is not particularly well understood, and there are a number of different types.
Toxic diffuse goitre or Graves disease, is a systemic autoimmune disease which involves the thyroid and the eyes.
Inflammation of the thyroid nodules (thyroiditis) may cause a release of stored thyroid hormone and be followed by a few months of hypothyroidism due to poor reserves of hormone.
Excessive iodine intake through using too much kelp, iodine rich foods or supplements.
Excessive use of other thyroid medications.
Other possible causes may well be immunological (precipitated by infection or a virus), or by trauma surgery, toxaemia radiation etc. or by one or more thyroid nodules over functioning for unknown reasons or by a problem in the pituitary gland as it is the pituitary that produces thyroid stimulating hormones. Any of these can cause the thyroid to overproduce the hormones thyroxine (T4) and triiodothyronine (T3), which in turn will produce symptoms of hyperthyroidism.
These symptoms are commonly palpitations, tremor, rapid heartbeat, warm and moist skin, nervousness, increased activity, increased sweating, fatigue, weight loss, insomnia etc.
Herbal treatment may include use of the herb Bugleweed (Hycopus virginicua) that has been shown to inhibit iodine metabolism and thyroxine release. Motherwort (Leonurus cardiaca) may also be used to help calm symptoms of palpitations etc. Other calming herbals may also be indicated.
I have heard of Vitex Agnus castus, Damiana and a herb called Erythacea centurea being used effectively, but have no personnal experience in using these herbs for this purpose and I’m not sure of the mechanism by which they would work, although I suspect by exerting an effect on the pituitary gland and hence on the thyroid.
Foods that are known to suppress thyroid action (known as goitrogens) are most green veges of the brassica family – brussel sprouts, cabbage, cauliflower, leeks etc. as well as turnips, spinach and soybean fibre, walnuts, peaches and pears. Including these in the diet may help. It is equally important to avoid iodine rich foods.
If there is inflammation present then supplementing with fish oils, Quercetin, vitamin C and E may help.