PIP: In order to provide information for the appropriate package insert labeling of progestin-only oral contraceptives (POC) in the US, a comprehensive review was made of norgestrel (0.075 mg) and norethindrone (0.35 mg), with the clinical differences indicated where applicable. The goal of this review was to cite primary sources for virtually all research specific to POPs since 1975. Conclusions and the types of studies which support these conclusions are given for each major section. The introductory chapter discusses the advantages and disadvantages of POCs and the magnitude and prevalence of their use. Future trends are also predicted. Chapter 2 considers the mode of action, including ovulation prevention; suppression of midcycle gonadotropin peaks; changes in cervical mucus, the endometrium, and the fallopian tubes; and clinical implications. Chapter 3 covers pharmacology (pharmacokinetics, pharmacodynamics and potency, and clinical implications). The next chapter presents information on efficacy and pregnancy outcomes in terms of pregnancy rates, compliance and efficacy, ectopic pregnancies, the outcome of pregnancies conceived while using POCs, and fertility following discontinuation. Chapter 5 focuses on metabolic effects, specifically lipid metabolism, carbohydrate metabolism and diabetes, coagulation factors, and blood pressure. Cardiovascular disease is considered in the next chapter, and chapter 7 presents findings on endometrial, ovarian, cervical, breast, and other cancers. A host of other medical considerations are discussed in chapter 8, including persistent ovarian follicles; reproductive tract infections; abnormal vaginal bleeding; uterine fibroids; gestational trophoblastic disease; benign breast disease; diseases of the liver, gallbladder, and bowel; endocrine dysfunction; epilepsy; bone density; sickle cell disease; ocular effects; surgery; and overdose. The last 4 chapters cover interactions with drugs and laboratory tests, common side effects, breast feeding, and effective use of POCs. Information on precautions and contraindications, indications, use instructions, and instructions for appropriate actions after missing a pill is appended.