The thyroid gland is an endocrine gland synthesizes thyroid hormones,   secreted into the blood stream and then carried to every tissue in the body. These thyroid hormones have a major impact on most body functions. For instances growth, use of energy and oxygen consumption, heat production, water and electrolytes homeostasis, modulate immunity, gonadal function and fertility and can alter the response the body toward different drugs. Hypothyroidism occurs when thyroxin levels drop to a point that the body begins to slow down its metabolic rate. Patients of hypothyroidism need to take compansatory thyroid hormones for the rest of their lives. The aim of present study is to investigate the effect of thyroid gland modulating drugs as (Eltroxin, thyroid hormone agonist and Carbimazol thyroid hormone antagonist) on the gonadal activity and reproduction aspects under the seasonal variation.