Data provided by Women on the Web, which offers abortion pills online, showed 5,650 women from both countries accessed the service from 2010 to 2015.
Most already have at least one child and a majority said taking the pills had been the right choice for them.
Laws in both countries ban or restrict access to abortion.
Abortion is legal in both countries if the mother's life it at risk. In Northern Ireland, it may also be permitted to preserve her physical or mental health.