How soon does an IUD become effective after you get it?

The non-hormonal IUD and two of the brands of the hormonal IUD (Liletta and Mirena) are effective immediately after they’re inserted. They actually work as very effective emergency contraception, preventing pregnancy from sex you’ve had in the 5 days before they are placed! The other hormonal IUDs, Kyleena and Skyla, are effective immediately if you get it inserted within 7 days of the start of your period, you’re switching from another method of hormonal birth control that you’ve been using consistently, it’s been less than 7 days since a first or second-trimester pregnancy ended, or you gave birth in the last 21 days. Otherwise, it takes 7 days after the IUD is inserted to be effective at preventing pregnancy, so you’ll need to use a backup method, such as condoms or internal condoms if you have sex during that time.