Estrogen causes hormonal birth controls’ most serious and rare side effects, such as stroke and heart attack. The hormone is also at the root of some of the contraceptives’ less serious but still annoying symptoms, including nausea and headaches.
Designing birth control that has a lower dose of estrogen but is still effective is an area of active research (SN: 8/22/17). Now, using a mathematical model, researchers have found that cutting the dose of estrogen in common contraceptives by 92 percent might still prevent pregnancy.