IUD insertion pain can vary from person to person. Unfortunately, there is not a great drug to take to make insertion less painful.
You can try taking ibuprofen beforehand the insertion and make sure you get the IUD inserted when your cervix is open, such as when you are on your period or ovulating. Even if there is some pain, it might be worth it for years of pregnancy-free sex.
References
- Family Planning NT. (2016). Intra Uterine Contraceptive Device (IUD or IUCD). Retrieved from http://www.fpwnt.com.au/365_docs/attachments/protarea/IUD-46c2853c.pdf