The FSRH has released a statement regarding quick starting contraception after using ellaOne. Basically ellaOne has an impact on progesterone receptors and there is concern that it may reduce the effectiveness of progestogenic contraceptives.
For this reason, the new advice is that hormonal contraception should not be started for at least 5 days after using ellaOne. This includes the COC, POP, implant and injectables.