SyreniRing is inserted at the start of a menstrual cycle and left in place for three weeks, followed by a ring-free week. The ring may be inserted and removed by the woman herself at home.
Clinical studies conducted in women aged 18–40 years showed that the contraceptive efficacy of the ethinylestradiol/etonogestrel vaginal ring appeared to be at least comparable with that of combined oral contraceptives.
Pearl Indices (number of pregnancies per 100 woman–years of use) in clinical studies of the ring were 0.96 (95% CI 0.64–1.39) in the intention to treat analysis (which takes into account user and method failure) and 0.64 (95% CI 0.35–1.07) in the per-protocol analysis (which takes into account method failure only) over 37,977 cycles and 28,723 cycles, respectively.
In a large study (n=1030) in which participants used either the ethinylestradiol/etonogestrel ring or a combined ethinylestradiol/levonorgestrel pill, the ring was associated with low incidences of breakthrough spotting or bleeding (2.0–6.4% over 13 cycles). Vaginal bleeding was exclusively restricted to the ring-free interval for most participants (58.8–72.8%).
The most frequently reported undesirable effects in the clinical trials of ethinylestradiol/etonogestrel were headache, vaginal infections and vaginal discharge, each reported by 5–6% of women.
No adverse effects of the ethinylestradiol/etonogestrel ring on bone mass were observed in a two-year study (n=107) in which it was compared to a non-hormonal IUD.