NuvaRing uses a type of progestin that may produce a slightly higher risk of blood clots than other progestins used in other types of hormonal contraception, though the data has not been confirmed. It mentions that in the fine print of the NuvaRing site here. (http://www.nuvaring.com/Consumer/commonQuestions/index.asp) (Scroll to the bottom.) However, NuvaRing is still on the whole a very safe type of contraception.