Background: The human thyroid gland is located in the front of neck. It consists of two lobes. The two lobes are joined with each other by isthmus.  The mood stabilizer Lithium Caronate has deleterious effects on the thyroid gland.

Aim: To observe   and report the data of the harmful effect of Lithium on the weight changes of   thyroid gland.

Methods: Sixteen rats were selected for this experimental study. The rodents were divided into two groups. Group A comprised of   eight animals which were given laboratory diet, Group B contained eight albinos who were given Tablet Lithium Carbonate in powder form at a dose of 60 mg/day for four weeks. After completion of the study time animals were sacrificed and thyroid gland weight were recorded and compared in both groups.

Results: The results in both groups were recorded and compared .It was reported that Group B animals had a highly significantly decreased thyroid weight after four weeks   Lithium ingestion than Group A control group.

Conclusion: The results of our study concluded that Lithium Carbonate   damages thyroid glandular tissue and causes its weight to decline.

Key words: Thyroid gland, Isthmus, deteriorating