Copper ions-releasing IUDs are more efficient thatn non-medicated methods. Why?

Explanation

Intra Uterine Devices (IUDs) are inserted in the uterus through vagina and are presently available as the non-medicated IUDs , copper releasing IUDs and hormone releasing IUDs Cu ions-releasing IUDs are more efficient methods because
(i) Cu ions released supperss sperm motility adn fertilising capacity of sperms
(ii) It increases phagocytosis of sperms within the uterus.
(iii) It is one of the safest. most effective, convenient and least expensive reversible contraceptives available.
(iv) It has no systemic effects and can be safely used by breast-feeding women.