"Oral contraceptives (OCs) of the combined type are "almost 100 percent effective" when "taken according to the prescribed regimen." But the oral contraceptives have disadvantages such as side effects during their early use. Moreover, their use is medically contraindicated for certain patients, particularly those with a history of thromboembolic disease.... [E]ven the theoretically most effective or highly effective methods of contraception are not always actually effective for a number of reasons. Except for voluntary sterilization which many people will not use, even the most effective or highly effective methods have shortcomings either in terms of method failures or in terms of side effects or medical contraindications. In addition some of the methods are so difficult to practice regularly and correctly that they have little practical utility."