Etonogestrel and ethinylestradiol concentrations were determined in 18 HIV+ women receiving desogestrel/ethinylestradiol (0.15/0.03 mg/day) and nevirapine (200 mg twice daily) and 14 HIV-negative women receiving desogestrel/ethinylestradiol (0.15/0.03 mg/day) alone. Etonogestrel and ethinylestradiol trough concentrations were decreased by 22% and 58% in the presence of nevirapine.
Significant decrease of ethinylestradiol with nevirapine, and of etonogestrel with efavirenz in HIV-positive women. Landolt NK, Phanuphak N, Ubolyam S, et al. J Acquir Immune Defic Syndr, 2014, 66(2): e50-2.

Coadministration of desogestrel/ethinylestradiol (0.15/0.03 mg/day) and nevirapine (200 mg twice daily) was studied in 18 HIV+ women. Serum progesterone was less than 1.0 ng/ml in all subjects. Nevirapine C12 concentrations increased by 17% but this was not statistically significant.
Efavirenz, in contrast to nevirapine, is associated with unfavorable progesterone and antiretroviral levels when coadministered with combined oral contraceptives. Landolt NK, Phanuphak N, Ubolyam S, et al. J Acquir Immune Defic Syndr, 2013, 62(5): 534-9.