There could be a number of causes, including heredity, certain foods or drugs, hormone levels, or hyperthyroidism. AnswerParty!
A thyroid disease is a medical condition impairing the function of the thyroid.
Virtually all the symptoms and signs of Graves' disease result from the direct and indirect effects of hyperthyroidism, with exceptions being Graves' ophthalmopathy, goitre and pretibial myxedema (which are caused by the autoimmune processes of Graves' disease). These clinical manifestations are dramatic and involve virtually every system in the body. The mechanisms that mediate these effects are not well-understood. The severity of the symptoms and signs of hyperthyroidism is related to the duration of the disease, the magnitude of the thyroid hormone excess, and the patient's age. There is also significant variability in the individual response to hyperthyroidism and individual sensitivity to thyroid hormone fluctuations generally. On top of that, Graves' disease patients can undergo periods of hypothyroidism (for further information, see symptoms of hypothyroidism): finding the right dosage of thyroid hormone suppression and/or supplementation can be difficult and takes time. The body's need for thyroid hormone can also change over time, like in the first months after radioactive iodine treatment (RAI). Thyroid autoimmune diseases can also be volatile: hyperthyroidism can interchange with hypothyroidism and euthyroidism.
Science of drugs including their origin, composition, pharmacokinetics,
pharmacodynamics, therapeutic use, and toxicology.
Pharmacology (from Greek φάρμακον, pharmakon, "poison" in classic Greek; "drug" in modern Greek; and -λογία, -logia "study of", "knowledge of") is the branch of medicine and biology concerned with the study of drug action, where a drug can be broadly defined as any man-made, natural, or endogenous (within the body) molecule which exerts a biochemical and/or physiological effect on the cell, tissue, organ, or organism. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function. If substances have medicinal properties, they are considered pharmaceuticals.