The Sound of Evolution
Norethindrone
Mechanism of action:
Norethindrone is a synthetic progestin and a derivative of 19-nortestosterone. Norethindrone suppresses the hypothalamic-pituitary-gonadal axis through negative feedback, reducing the luteinizing hormone (LH) surge and preventing normal follicular rupture, thereby inhibiting or delaying ovulation. Norethindrone also thickens cervical mucus, making it more difficult for sperm to pass through the cervix into the uterine cavity and reducing the likelihood of fertilization. In addition, norethindrone keeps the endometrium in a thin, non-proliferative state, which makes embryo implantation less favorable even if fertilization occurs.
Reference(s):
1. Stanczyk FZ et al. (1990). Metabolism of levonorgestrel, norethindrone, and structurally related contraceptive steroids. Contraception.
2. Frohlich M et al. (2004). In vitro and ex vivo evidence for modulation of P-glycoprotein activity by progestins. Biochem Pharmacol.