This study is for adults 18-74 years with a condition called Congenital Adrenal Hyperplasia (CAH) caused by 21-hydroxylase deficiency (21-OHD). CAH is a disorder affecting the adrenal glands, which produce important hormones. The study wants to see how well a drug called atumelnant works and if it is safe. It's a "Phase 3" study, meaning it is in the advanced stages of testing. Participants will either receive atumelnant or a placebo (a harmless pill with no effect), and neither the participants nor the researchers will know who gets which. You must have been on stable glucocorticoid (GC) treatment, like hydrocortisone, for at least two months to join. The study will last several months, including a 3-6 week screening phase to see if you're eligible. Approximately 150 participants will be chosen.

• The study includes about 150 participants and lasts several months.
• You must be on stable hormone therapy to participate.
• Participants will receive either atumelnant or a placebo.