Explain what? That there are medical conditions requiring hormones that equate to birth control? Or that people have medical conditions that could cause serious harm to self or child if they would conceive?
You can Google stuff for your self. There are numerous conditions - numerous. And also there are many meds people are on that cause birth defects so people choose not to become pregnant with a child they are pretty confident will have serious birth defects.
You can Google that too. Simple search - medications and birth defects. Duh.