Low-dose oral minoxidil is a pill version of Rogaine. It's used off-label for hair loss and is often more effective — and far easier to stick with — than the topical, because there's no daily scalp application.
Oral tranexamic acid is a clotting medication used off-label for melasma. It's one of the few treatments that addresses the blood-vessel side of melasma — a piece of the problem most brighteners ignore.
Spironolactone is a pill that blocks androgens (male hormones). Originally a heart medication, it's now widely used off-label in women for hormonal acne, hair loss, and unwanted facial hair.