Both hypothyroidism and hyperthyroidism can cause hair loss in acute circumstances. Hypothyroidism is caused by underactive thyroid and it deteriorates the health of the hair by making it brittle, dry and thin.
Although it is difficult to establish whether the medication causes this or the changes in the thyroid, but generally the anti-thyroid drugs are not responsible.
The hair follicles on the scalp have a very unique behavior. The growth is not continuous but occurs in phases and there are gaps. The hair grows in length in active phase and the hair is lost plus replaced in the rest phase. It is common to lose hair during the times of illness or after them because the stress of the disease puts pressure and causes the follicles to be in the rest stage.
You will be glad to know that in most cases of hypothyroidism, the hair loss is temporary. After the treatment of the illness, drugs can be used to improve hair growth but it can be slow. The slow life cycle of the hair with longer rest phases is what causes the delay.
With proper self-care methods including hair loss supplements and keeping adrenal fatigue under observation, the health of the hair can be restored.