Obesity has been defined as a body mass index (BMI) greater than 30 kg/m2 and is becoming a leading cause of preventable death. A significant cause of obesity development is an imbalance between energy intake and expenditure. Cellular respiration and thermogenesis modulate resting metabolic rate, and thyroid hormones impact energy expenditure. Thyroid hormones affect appetite regulation and modulate lipid turnover in adipocytes. Many health disorders have been linked to obesity, which causes a burden on the individual as well as the community. Preventable diseases such as type 2 diabetes, hypertension, hypercholesterolemia, hypertriglyceridemia, and nonalcoholic fatty liver disease are associated with overweight and obesity. Moreover, obesity can influence thyroid function in various clinical presentations, such as subclinical Hypothyroidism, which may cause alterations in basal metabolic rate with a consequent increase in BMI, and overt Hypothyroidism, in which obesity may be a presenting feature. This review focuses on the effect of Thyroxine treatment for overt and subclinical Hypothyroidism on body mass and obesity.