A pregnant woman with hypertension is switched from enalapril to methyldopa. ACE inhibitors are teratogenic (fetal kidney damage) — pregnancy hypertension uses methyldopa, nifedipine, or labetalol instead. The principle: every drug in pregnancy is a two-patient decision — benefit must clearly outweigh fetal risk; FDA's old A/B/C/D/X is replaced by narrative labeling, but the caution stands. Preconception counseling (folic acid, stopping valproate/isotretinoin) prevents the preventable.