An analysis of 570 HIV-infected women in Swaziland using levonorgestrel implant and lopinavir/ritonavir, nevirapine or efavirenz based regimens showed that none of the women on nevirapine (n=208) or lopinavir (n=13) became pregnant whereas 15/121 (12.4%) women on efavirenz became pregnant. This study suggests that nevirapine may not impair the efficacy of levonorgestrel implant.
Implementing the Jadelle implant for women living with HIV in a resource-limited setting: concerns for drug interactions leading to unintended pregnancies. Perry SH, Swamy P, Preidis GA, et al. AIDS, 2014, 28(5): 791-793.

The effect of efavirenz- or nevirapine-based antiretroviral therapy (ART) coadministration on levonorgestrel pharmacokinetics was studied in three groups of HIV-infected Ugandan women: ART-naive (n=17), efavirenz-based ART (n=20), and nevirapine-based ART (n=20). Levonorgestrel implants were inserted at baseline in all women. In one year of combined use, levonorgestrel exposure was markedly reduced in participants who received efavirenz-based ART, accompanied by contraceptive failures. In contrast, nevirapine-based ART did not adversely affect levonorgestrel exposure or efficacy. At week 24, levonorgestrel concentration were 47% lower in the efavirenz group, and 35% higher in the nevirapine group when compared to the ART-naive group (geometric mean levonorgestrel concentrations 528, 280, and 710 pg/ml in the ART-naive, efavirenz, and nevirapine groups, respectively). At week 48, levonorgestrel concentration were 57% lower in the efavirenz group, and 14% higher in the nevirapine group when compared to the ART-naive group (levonorgestrel concentrations 580, 247, and 664 pg/mL in the ART-naive, efavirenz, and nevirapine groups, respectively). Three pregnancies (3/20, 15%) occurred in the efavirenz group between weeks 36 and 48. No pregnancies occurred in the ART-naive or nevirapine groups.
Unintended pregnancies observed with combined use of the levonorgestrel contraceptive implant and efavirenz-based antiretroviral therapy: a three-arm pharmacokinetic evaluation over 48 weeks. Scarsi KK, Darin KM, Nakalema S, et al. Clin Infect Dis, 2016, 62(6): 675-82.

Oral contraceptives and other hormonal methods of birth control, other than DMPA, should not be used as the sole method of contraception in women taking nevirapine, since nevirapine might lower the plasma concentrations of these medications. Appropriate doses for hormonal contraceptives (oral and other forms of application) other than DMPA in combination with nevirapine have not been established with respect to safety and efficacy. Additionally, when post menopausal hormonal therapy is used during administration of nevirapine, its therapeutic effect should be monitored. Viramune Summary of Product Characteristics, Boehringer Ingelheim International GmbH, January 2012.

Oral contraceptives and other hormonal methods of birth control, other than DMPA, should not be used as the sole method of contraception in women taking nevirapine, since nevirapine may lower the plasma levels of these medications. An alternative or additional method of contraception is recommended. Additionally, when oral contraceptives are used for hormonal regulation during nevirapine therapy, the therapeutic effect of the hormonal therapy should be monitored.
Viramune Prescribing Information, Boehringer Ingelheim Pharmaceuticals Inc, November 2011.