Copper-T, an intrauterine device (IUD), is contraindicated in trophoblastic diseases. These diseases, such as hydatidiform mole, involve abnormal growth of the trophoblast cells, and the use of Copper-T could worsen the condition. It should not be used in such cases. Copper-T is a safe and effective form of contraception for most women but is contraindicated in certain conditions like trophoblastic diseases.