Abstract The effects of steroidal and nonsteroidal oral contraceptives on histological changes in the thyroid were studied in female Wistar albino rats for 30 days. The steroidal combined oral contraceptive pill ( norgestrel + ethinylestradiol ) was diluted to 0.14mg/ ml (Low Dose ) , 0.21 mg/ml (dose as per literature ), and 0.43 mg/ ml ( high dose ). After 30 days of administration of steroidal oral contraceptives at a dose of 0.21 mg/ml/rat/day, follicular colloid levels decreased and follicular cell hypertrophy occurred. In the present study, rats given 0.29 mg/ml/rat/day and 0.43 mg/ml/rat/day non-steroidal tablets exhibited hyperactivity and were filled with colloidal material, but were moderately active. Further research is needed to calculate the perfect dose that does not cause side effects.