Shifting from Oral Contraceptives to Norethisterone Acetate, or Vice Versa, because of Drug Intolerance : Does the Change Benefit Women with Endometriosis?

Background/Aims: Oral contraceptives (OC) and norethisterone acetate (NETA) are among first-line medical therapies for symptomatic endometriosis, but their use is sometimes associated with intolerable side effects. We investigated whether shifting from low-dose OC to NETA (2.5 mg/day), or vice versa, improved tolerability. Methods: Sixty-seven women willing to discontinue their treatment because of intolerable side effects despite good pain relief, were enrolled in a self-controlled study, and shifted from OC to NETA (n = 35) or from NETA to OC (n = 32). The main study outcome was satisfaction with treatment 12 months after the change. Tolerability, pain symptoms, health-related quality of life, psychological status, and sexual functioning were also evaluated. Results: After treatment change, good tolerability was reported by 37% of participants who shifted to NETA, and by 52% of those who shifted to OC. At 12-month assessment, 51% of women intolerant to OC were satisfied with NETA, and 65% of those intolerant to NETA were satisfied with OC (intention-to-treat analysis). Other study variables did not vary substantially. Conclusions: In selected endometriosis patients, shifting from OC to NETA, or vice versa, because of side effects, improved tolerability. Better results were observed when substituting NETA with OC rather than the other way round.