IUDs work mechanically by inhibiting implantation of the zygote in the womb.¹ Contrast, the pill, which prevents contraception with hormones. This means your mood cycle will change less with IUDs

Note that some IUDs include a hormone component. Discuss with your doctor what is your best choice.

This also means complications with IUDs are also mechanical, most commonly unintended eviction. In prior eras, sone IUDS could scrape or puncture the uterus, but their design is vastly improved so its extremely rare.

¹ Yes, this freaks out the anti-abortion-access and anti-contraception-access crowds since they assert personhood at conception. To that, I offer this statistic from the Guttmacher Institute: 75% of all conceptions fail to result in live birth. By far the majority of them are due to failure to implant. Selection is intrinsic to the human reproductive process.

This also means the most populous place in the Christian Cinematic Universe is the Limbo of the innocents, on the fringe of Hell, at 300 billion souls, most of whom never breathed air. Unless Limbo is not cannon, in which case they go to the Hell of the Damned totalling 400 billion souls. Its awkward.