Will a copper iud work as emergency contraceptive 6 days after having unprotected sex?

"Iffy": Eight days after conception may or may not prevent a fertilized ovum from implanting inside the uterus. A IUD is designed to produce early abortion of a recently implanted fertilized ovum or prevent implantation completely.

Not well studied: The copper IUD is the most effective method of emergency contraceptive if inserted within 5 days of unprotected intercourse. Some providers will consider insertion within 7 days for this purpose, but it's not well-known how effective it is beyond 5 days. There is unfortunately no emergency contraceptive approved for use beyond 5 days of intercourse.