I've had the copper coil for 3 years. The only side effect I have is very heavy periods for a couple days each cycle.
I usually wear a mooncup, cloth sanitary pad AND period pants on those days.
My period started yesterday and today it's heavy as expected. I'm not wearing a mooncup as just in the house so easy enough to change he CSP.
Holy crap there's even more blood than normal. I've had to change the pad 4 times in 90 minutes, and each time there's been a huge clot. About the size of a small mouse (sorry - can't think of anything else). I can actually the feel the clots coming out 🤢
I don't imagine it'll be like this for more than 48h - but that's a lot of blood to lose is it not?
I had bloods taken recently and my iron was a little low but my blood count was fine so they weren't too concerned.