A study in the BMJ, with over 1.6 million women, found that users of vaginal rings with ethinyl estradiol and etonogestrel have a 6.5 times increased risk of venous thrombosis compared to non-users.
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NuvaRing is contraindicated for a risk of blood clots that is specific to NuvaRing's class of contraceptives.
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A study by Danish researcher Dr. Øjvind Lidegaard in 2012 with 1.6 million women found a 6.5 times increase in the likelihood of venous thromboembolism when compared to users of non-hormonal based birth control.